Ashya King's father has said he and his wife are "very relieved to be free" after being released from a Spanish jail.
Brett King said he could not wait to see his son and offered his thanks to the Spanish and British people.
"We are very grateful to Spain for the support and help we have received," Mr King told reporters.
"We will go to see my son as soon as possible, we have been dying to see his face for so long. Thank you to Spain for helping us and thank you to England too," he added.
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.