THE sobbing brother of a Harry Potter star has revealed the moment he realised the actor had been stabbed to death.
Rob Knox, 18, was knifed five times by Karl Bishop outside the Metro Bar in Sidcup, South East London, in May 2008.
He had heroically intervened to protect his brother Jamie, then 17, who was being threatened by a thug with two kitchen knives.
Tragically, Rob had just finished filming on the sixth Harry Potter film in his role as Marcus Belby days before the horror unfolded.
A new ITVX documentary will air tomorrow exploring the brutal killing with interviews from his family and co-stars.
Brother Jamie also breaks down as he reveals Rob's heartbreaking final moments.
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He tells the show: "I remember hugging mum. As I was hugging her, I could see over her shoulder.
"I think in my heart I probably knew he was dead then. So that was hard to see."
Rob had headed out with pals on May 24, 2008 - four days after filming wrapped - to celebrate with pals at his local.
He called Jamie saying to head down as he wanted his brother to be there.
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He headed to the bar and noticed a man yelling at their girl mates when an "altercation" broke out and someone was punched.
Bishop, then aged 22, fled the scene before returning with two knives threatening to "stab anyone who came near him".
Hearing of the row outside, brave Rob went out to protect Jamie when Bishop knifed him.
Shockingly, the killer had only recently been released from prison after another stabbing.
In a harrowing 999 call played in the show, one of Rob's friends can be heard begging police to come as the killer stalked outside with the knives.
He said: "He's got two knives on him, waving them about, waving them in my face.
"My mate had a punch up with him earlier, the police came, it was all calmed down, now the ****** come down with two knives."
Rob, who also had roles in ITV's The Bill, Channel 4's Trust Me, I'm a Teenager, and Junior Masterchef, sadly couldn't be saved.
He never got to see his performance in Harry Potter as it aired a year after his death.
Tragically, the rising star had signed up for the final two films and was on the cusp of a global breakthrough.
Tom Felton, who played Draco Malfoy in the series, opens up about Rob's killing in the documentary.
The actor, who used to play cricket with Rob in the car park of Leavesden Studios, said the murder was "beyond belief".
Tom added: "I hadn't heard of that happen to a friend of mine or someone I worked with.
"He was definitely not the sort of character in my mind to have got involved in something like that at all so to hear his life had come to an end in that manner was distressing."
Bishop was found guilty of murder in March 2009 and was handed a life term with a minimum sentence of 20 years.
He was also given three further concurrent life sentences for wounding.
Following Rob's death, his family set up the Rob Knox Foundation to help young people get into acting and tackle knife crime.
His dad Colin said: "We knew we could rant and rave and solve nothing, or we could try to oppose knife crime.
"Our stance has always been to use Rob's legacy to focus on what we can do. But I also wanted the documentary to show what a great lad Rob was; that he was a living, breathing person who was taken away.
"He was exceptional."
- (K)nox: The Rob Knox Story will be available from Thursday on ITVX.