Sometimes a story hits you in a way you don’t expect. That’s what many Harry Potter fans said after watching a documentary about Rob Knox, the young actor whose life ended far too soon. His bright future made the tragedy feel even heavier.

Rob Knox was only 18 when he was killed in 2008. He had just finished filming Harry Potter and the Half-Blood Prince, where he played Marcus Belby, and was preparing to return for the final movie. For many viewers, seeing his excitement and talent captured on screen now feels deeply bittersweet.

The documentary, (K)nox: The Rob Knox Story, aired on ITV and features emotional interviews with his co-stars, including Tom Felton and Jim Broadbent. It walks through Rob’s childhood, early acting work, and the night everything changed. He died protecting his younger brother during a fight outside a bar in Sidcup, London.

Fans who watched the documentary said they cried throughout. Many admitted they never knew Rob had passed away, and the revelation left them stunned. Their messages online echoed the same feeling—a young life lost for no reason.

Even the Harry Potter cast shared heartfelt tributes after his death. Daniel Radcliffe wrote that they were “devastated to have lost you,” while Rupert Grint called it an honor to have known him. Their words show how deeply Rob touched those around him.

Rob’s killer is serving a long sentence, but the pain of his loss remains. The documentary now serves as both a tribute and a reminder to cherish the people we still have beside us.