Actor Tom Felton has spoken about the moment he found out his Harry Potter co-star Rob Knox was murdered.

Although Knox only had a brief appearance as Ravenclaw student Marcus Belby, he and Felton would hang out together after filming and play pranks on the rest of the cast.

This made it even harder for Felton understand what had happened to his co-star.

After filming had finished, Knox enjoyed a night in Sidcup with his friends and his younger brother Jamie - when an older man approached them with two kitchen knives.

In the ensuing scuffle, Knox was stabbed five times and lost his life protecting his brother.

“We were just mucking around in the carpark two days ago, it was beyond belief, to be honest with you – especially in the way that it happened,” explained Felton, as he appeared in a documentary about the Knox’s short life.

The loss of his friend was devastating for Felton, with the actor saying that it was the first time he had experience knife crime.

“I hadn’t heard of a friend of mine or someone that I worked with and he was definitely not the kind of character in my mind that would've got involved in something like that,” he added.

"To hear that his life had come to the end, in that manner, it was distressing I think for all of us."

Whilst Knox’s killer, Karl Bishop, would be sentenced to 20 years in prison for the murder – it left a lasting impact on the cast.

Nearly two decades on and former cast members are appearing in an award-winning documentary about Knox’s short life and his untimely death.

The film is now available to stream and watch on ITVX.