Ashya King's brother says his parents are surprised by the mass of reporters outside their prison, adding: "None of us thought this would be international news."
Danny King told BBC News that he had been speaking to his mother and father by phone, who, despite the shock, were "just happy that they can go and see Ashya".
Asked if Ashya would go to Prague, he said: "I don't know, because we've had different offers from treatment centres in America, my parents haven't been able to look at that, at the end of the day it's their decision which centre they will be able to get that treatment."
Earlier Danny's other brother Naveed expressed his joy on Facebook at news of his parents' release.
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The head of the police force which applied for a European Arrest warrant against the parents of Ashya King has now urged their release.
A British mother whose son's life was saved by proton therapy has told ITV that she defied NHS doctors' advice to pursue the treatment.
The parents of Ashya King said they took him out of a hospital to seek proton beam treatment which is not available under the NHS.