The woman in charge of the medical centre in Prague that treated brain cancer survivor Ashya King has said she is "over the moon" with his progress.
Iva Tatounova said the six-year-old's recovery was more proof that proton beam therapy should be "the first choice" of treatment for children with his condition.
Ashya's parents Brett and Naghmeh King took their son back to the centre in the Czech capital, one year after they sparked a Europe-wide manhunt when they removed him from a UK hospital.
Ms Tatounova, director of the Proton Therapy Centre, told ITV's Good Morning Britain: "He's doing fantastically. I'm over the moon actually. He walked to the centre on his own feet. He didn't need a wheelchair.
"He's speaking and playing with other kids and his siblings, and next week (he's) going, for the first time, to a school."
Ms Tatounova said proton beam therapy - which is not widely available in the UK - "should be the first choice of treatment" for young children with brain cancer "because it's less aggressive".
"It's already proven, not only with Ashya's case, but even 10 years ago," she said. "These problems are nothing new to this world. This is no experiment.
"Proton therapy again proved its advantages over other treatments. I hope we are able to help more UK patients."
Police launched an international search for the King family after Ashya was removed from Southampton General Hospital without doctors' consent in August last year.
Mr and Mrs King were arrested a few days later in Spain, where they were forced to spend several nights in prison away from their son before being released.
A High Court judge later approved the move to take Ashya to Prague for proton therapy.
The treatment limits the collateral damage of radiation to other vital organs, such as the heart and liver in Ashya's case, and can lead to less severe long-term side-effects including heart and breathing problems.
The therapy was not offered to Ashya on the NHS, although the health service later agreed to fund his treatment. Several new proton beam therapy centres will open in the UK from next year.
Ashya's grandmother Patricia King has previously described the authorities' handling of the case as a "huge injustice".