Ashya King was rushed to a specialist hospital in Malaga for urgent medical treatment while his parents Brett King, 51, and Naghemeh King, 45, were detained by officers in Spain.
The family were discovered after they checked into Hostel Esperanza in Benajarafe.
Earlier, Mr King, 51, released a 10-minute video on You Tube. In the clip, Mr King lies on a bed with his son Ashya between his legs. Ashya is attached by a tube to a drip on the side of the bed.
Speaking directly to the camera, Mr King pleads with police to call of their international search, which was launched after Ashya was taken from Southampton General Hospital on Thursday.
He said he wanted Ashya to have Proton Beam therapy which is not available for the treatment of brain cancer in the UK and therefore had no choice but to take him out of the hospital.
Mr King claimed that when he told doctors he did not want Ashya to have the treatment they recommended, they were threatened with an emergency protection order, which would have prevented them from seeing their son.
“Proton beam is so much better for children with brain cancer,” he said in the clip. “It zones in on the area, whereby normal radiation passes right through his head and comes out the other side and destroys everything in his head.
“So we pleaded with them for proton beam treatment. They looked at me straight in the face and said with his cancer - which is called medulloblastoma - it would have no benefit whatsoever."
Mr King said his son's treatment seemed like "trial and error" and claimed he was told if he questioned the treatment the hospital would seek an emergency protection order.
He said: "After that I realised I can't speak to the oncologist at all, because if I actually ask anything or give any doubt I wasn't in full accord with them, they were going to get a protection order which meant in his deepest, darkest hour I wouldn't be there to look after him, and neither would my wife - they would prevent us from entering the ward.
"That's such a cruel system I decided to start looking at the proton beam myself."
He added: "We decided to try and sort it out ourselves but now we're refugees almost.
Brett King explains why he has taken Ashya out of UK
"We can't do anything. The police are after us. The things we want to do to raise the money to pay for the proton beam, they've prevented it now.
"So my son is being treated and he's doing fine. We're very happy with his progress. We're not neglecting him. He has everything he had in hospital."
On Saturday, police obtained a European arrest warrant. Officers said the warrant was obtained on the grounds of neglect but it would be used only as a last resort.
They said they “would much prefer for the parents to come forward voluntarily”.
Police had raised concerns about Ashya’s battery-operated feeding tube, which they said would have run out on Friday night. They said it could be replaced only by medical experts, leading police to warn that “time is running out” for the youngster.
But Mr King said the family had enough feeding packs and Calpol to care for their son.
“We were most disturbed today to find his face is all over the internet and newspapers and we have been labelled as kidnappers, putting his life at risk, neglect," he said.
"As you can see there's nothing wrong with him, he is very happy actually since we took him out of hospital," Mr King said.
"He has been smiling a lot more, he has very much been interacting with us."
Mr King said his son was treated by Dr Gary Nicolin, a consultant paediatric oncologist with over 25 years’ experience.
Dr Nicolin, who has worked at the hospital for the last decade, has previously worked in Canada and South Africa.
Mr King said he told doctors he would pay for the treatment himself.
Mr King said Ashya was "responding so much better" than he did in hospital.
"We couldn't take it any more - not knowing and not being able to question anything in fear that they say, 'Sorry Mr and Mrs King, emergency protection order, you're no longer allowed in the ward'," he said.
"Under that stress, our son has grade four brain tumour, we couldn't discuss or question them at all in fear that our son would be in that ward all day long by himself without his parents being able to come in.
"We couldn't be under that system any more.
"I was going to get the money to pay for the proton beam therapy but they have prevented that now because the Spanish police are involved and I can't do want I wanted to do."
Mr King urged police to call off "this ridiculous chase".
"We're not neglecting our son, he's in perfectly good health," he said.
"My son is smiling, he's happy, we're doing things as a family. We just want to be left in peace. He's very sick. I just want to get on with his treatment. I'm not coming back to England if I cannot give him the treatment I want, which is proper treatment.
"I just want positive results for my son."
According to Cancer Research UK, Proton Beam therapy is a highly-targeted type of radiotherapy that can treat hard-to-reach cancers, such as spinal tumours (chordomas), with a lower risk of damaging the surrounding tissue and causing side effects
The Kings' eldest son was caring for his siblings while his parents were held at a police station in nearby Velez-Malaga.
Mr and Mrs King were expected to be taken to Madrid on Sunday for an extradition hearing at Madrid's Central Criminal Court.
Assistant Chief Constable Chris Shead of Hampshire Constabulary said the boy's parents had been arrested at 10pm local time after Spanish police stopped the family's vehicle.
"We don't have many details on Ashya's condition at this point in time but what we do know is that he was showing no visible signs of distress," Mr Shead said.
"Ashya has now been taken to a hospital in Malaga. The parents have been arrested. They have been taken to a police station."
Spanish police were acting on a European arrest warrant requested by Hampshire Constabulary when they arrested the Kings.
When they stopped the family's Hyundai people carrier officers found Ashya and his parents inside.
Mr Shead said: "There are no winners in this situation. I've said all along that this must be a terribly distressing time for Ashya's family and I stand by that now."
He added that it was too soon to say when Ashya would come back to the UK but Southampton General Hospital have been contacted so they can liaise with the medical taking care of him in Spain.
"Ashya's brothers and sisters were not in the vehicle," Mr Shead said. "We have located them. They're all okay, they're fine. They are actually in a hotel about 10 miles away."
He also said that a team of Hampshire police officers would be going to Spain tomorrow to continue the investigation.
No one from Southampton General Hospital was available for comment.
Mr King claimed that when he told doctors he did not want Ashya to have the treatment they recommended, they were threatened with an emergency protection order, which would have prevented them from seeing their son.
“Proton beam is so much better for children with brain cancer,” he said in the clip. “It zones in on the area, whereby normal radiation passes right through his head and comes out the other side and destroys everything in his head.
“So we pleaded with them for proton beam treatment. They looked at me straight in the face and said with his cancer - which is called medulloblastoma - it would have no benefit whatsoever."
Mr King said his son's treatment seemed like "trial and error" and claimed he was told if he questioned the treatment the hospital would seek an emergency protection order.
He said: "After that I realised I can't speak to the oncologist at all, because if I actually ask anything or give any doubt I wasn't in full accord with them, they were going to get a protection order which meant in his deepest, darkest hour I wouldn't be there to look after him, and neither would my wife - they would prevent us from entering the ward.
"That's such a cruel system I decided to start looking at the proton beam myself."
He added: "We decided to try and sort it out ourselves but now we're refugees almost.
Brett King explains why he has taken Ashya out of UK
"We can't do anything. The police are after us. The things we want to do to raise the money to pay for the proton beam, they've prevented it now.
"So my son is being treated and he's doing fine. We're very happy with his progress. We're not neglecting him. He has everything he had in hospital."
On Saturday, police obtained a European arrest warrant. Officers said the warrant was obtained on the grounds of neglect but it would be used only as a last resort.
They said they “would much prefer for the parents to come forward voluntarily”.
Police had raised concerns about Ashya’s battery-operated feeding tube, which they said would have run out on Friday night. They said it could be replaced only by medical experts, leading police to warn that “time is running out” for the youngster.
But Mr King said the family had enough feeding packs and Calpol to care for their son.
“We were most disturbed today to find his face is all over the internet and newspapers and we have been labelled as kidnappers, putting his life at risk, neglect," he said.
"As you can see there's nothing wrong with him, he is very happy actually since we took him out of hospital," Mr King said.
"He has been smiling a lot more, he has very much been interacting with us."
Mr King said his son was treated by Dr Gary Nicolin, a consultant paediatric oncologist with over 25 years’ experience.
Dr Nicolin, who has worked at the hospital for the last decade, has previously worked in Canada and South Africa.
Mr King said he told doctors he would pay for the treatment himself.
Mr King said Ashya was "responding so much better" than he did in hospital.
"We couldn't take it any more - not knowing and not being able to question anything in fear that they say, 'Sorry Mr and Mrs King, emergency protection order, you're no longer allowed in the ward'," he said.
"Under that stress, our son has grade four brain tumour, we couldn't discuss or question them at all in fear that our son would be in that ward all day long by himself without his parents being able to come in.
"We couldn't be under that system any more.
"I was going to get the money to pay for the proton beam therapy but they have prevented that now because the Spanish police are involved and I can't do want I wanted to do."
Mr King urged police to call off "this ridiculous chase".
"We're not neglecting our son, he's in perfectly good health," he said.
"My son is smiling, he's happy, we're doing things as a family. We just want to be left in peace. He's very sick. I just want to get on with his treatment. I'm not coming back to England if I cannot give him the treatment I want, which is proper treatment.
"I just want positive results for my son."
According to Cancer Research UK, Proton Beam therapy is a highly-targeted type of radiotherapy that can treat hard-to-reach cancers, such as spinal tumours (chordomas), with a lower risk of damaging the surrounding tissue and causing side effects
The Kings' eldest son was caring for his siblings while his parents were held at a police station in nearby Velez-Malaga.
Mr and Mrs King were expected to be taken to Madrid on Sunday for an extradition hearing at Madrid's Central Criminal Court.
Assistant Chief Constable Chris Shead of Hampshire Constabulary said the boy's parents had been arrested at 10pm local time after Spanish police stopped the family's vehicle.
"We don't have many details on Ashya's condition at this point in time but what we do know is that he was showing no visible signs of distress," Mr Shead said.
"Ashya has now been taken to a hospital in Malaga. The parents have been arrested. They have been taken to a police station."
Spanish police were acting on a European arrest warrant requested by Hampshire Constabulary when they arrested the Kings.
When they stopped the family's Hyundai people carrier officers found Ashya and his parents inside.
Mr Shead said: "There are no winners in this situation. I've said all along that this must be a terribly distressing time for Ashya's family and I stand by that now."
He added that it was too soon to say when Ashya would come back to the UK but Southampton General Hospital have been contacted so they can liaise with the medical taking care of him in Spain.
"Ashya's brothers and sisters were not in the vehicle," Mr Shead said. "We have located them. They're all okay, they're fine. They are actually in a hotel about 10 miles away."
He also said that a team of Hampshire police officers would be going to Spain tomorrow to continue the investigation.
No one from Southampton General Hospital was available for comment.
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