"Everything is improving with Ashya," his father Brett told reporters in Prague while the six-year-old smiled and walked around on unsteady legs. A year earlier he had only been able to open his eyes.
"His walking is improving, his coordination is improving, his speaking is improving, his writing and drawing skills are improving but he is a little bit behind," Brett added outside the hospital where Ashya had received the so-called proton therapy.
"I'm sure in the years to come he will catch up and be like a normal child," he said before taking Ashya on a walk along the historic Charles Bridge in the city centre.
Ashya's case made headlines when his parents removed him from a British hospital against the doctors' orders in August 2014, sparking an international manhunt.
The Kings feared traditional radiotherapy would damage his brain and opted instead for the proton therapy, unavailable in Britain but touted as more precise because it only targets malignant cells.
Brett and Naghemeh King were taken into custody in Spain on an international warrant as British authorities suspected they were not acting in the best interests of their child.
But after they spent four days in a Spanish prison, a British court reunited them with their son at a Spanish hospital and allowed them to travel to Prague where he spent almost 50 days.
Ashya was declared cancer-free in March, almost half a year after undergoing 30 sessions of proton therapy with a beam targeting his brain tumour.
The King family were photographed on returning to Prague. Photo: Michal Cizek / AFP
"His progress seems to come in jumps, it's not continual, so he might plateau out for some time but suddenly he'll do something that takes him onto the next level," Brett said as Ashya stumbled down the 500-metre (0.3-mile) bridge with the help of his parents and siblings.
"There's a lot of things he could do but we're just very careful with him, we want the progress to be without him injuring himself so we don't take any risks whatsoever."