The father of Harry Potter actor Robert Knox told a memorial service that his son was "living his dream" when he died.

Speaking at his son's funeral, Colin Knox described his family's "living nightmare" since his son's death.

The 18-year-old was stabbed outside a bar in Sidcup, south east London, last month.

He played wizard Marcus Belby in the forthcoming film Harry Potter And The Half-Blood Prince.

Rupert Grint, who played Ron Weasley in the film, joined hundreds of friends and family at St John the Evangelist Church in Sidcup.

Mr Knox, 55, said there were "no words" to describe how his wife, Sally, and their other son Jamie, felt at their loss.

He said Robert always thought of other people before himself and urged the teenager's friends to "hold Robert in your hearts".

He said: "The loss is so powerful... it's like having a nightmare, in fact it is a nightmare - we live it every day.

"But there's no waking up from it, feeling relief and you never revert back to normal."

He said he would miss his son's "smile, humour and laughter" and fought back tears as he told stories from Robert's childhood.

Mr Knox added: "Rob loved the part of Marcus Belby. He loved being part of the international iconic story of Harry Potter. He was always talking about the people he worked with."

He went on: "If there's a piece of Rob in you, then take that with you for the rest of your life and keep it for Rob.

"If you saw things in Rob that embraced your heart, then embrace them."

© Independent Television News Limited 2009. All rights reserved.