Police in Spain yesterday released the parents of the five-year-old after they were detained there under a European arrest warrant for taking their child out of the University Hospital Southampton without the consent of doctors due to concerns over the treatment he was receiving.
Daniel King told the BBC he had seen his brother, who is now being treated at a hospital in Malaga, southern Spain, yesterday, and said that he was physically "fine" but "emotionally very confused."
"The reason we chose Prague is because it's the best solution in Europe and also cheaper than going to America," he explained.
Grandmother Patricia King added that Ashya would not be able to cope with the pressure on board a long-haul flight.
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Brett King, 51, took his son out of the southern England hospital last week after he claimed doctors had blocked his attempts to take Ashya abroad for proton beam therapy.
He also claimed that doctors had threatened to ask for a protection order and take the child away if he interfered with his treatment plan.
It said proton therapy would be a suitable method of treatment for Ashya, but that he would need to go back to England first to undergo two cycles of chemotherapy.
"Ashya shall go for proton therapy to the Czech Republic," said Jiri Kubes, head of proton therapy at the centre.
The case prompted an outcry in Britain, where some 130,000 people signed a petition calling for the boy to be reunited with his parents.
Grandmother Patricia King argued that the warrant should never have been issued and accused Hampshire Constabulary and Southampton General Hospital of dealing in "lies and then U-turns."