Happier times: A 'crushed' Mark Speight says he can no longer perform in the BBC show SMart

Speight said the "tragic loss" of Natasha Collins had left him unable to continue.

Collins, a 31-year-old actress and presenter, was found dead at the couple's London flat on January 3.

A post-mortem examination was "inconclusive" and further toxicology tests are due to take place.

Speight was initially arrested on suspicion of murder and supplying Class A drugs.

Police are no longer treating him as a murder suspect but he is bailed to return on the drugs matter next month.

The presenter has insisted he had nothing to do with his fiancee's death.

He co-hosted CBBC show SMart with Kirsten O'Brien and she will continue as presenter.

In a statement released today, Speight said: "The tragic loss of Tash has affected her family and me very deeply and therefore I feel unable to commit to the next series of SMart, which is about to start filming.

"I do wish Kirsten and all the team all the very best."

A friend said: "Mark is absolutely crushed by what happened to Natasha and is unable to contemplate going back to work at the moment."

Scroll down for more...

Tragic: Actress and presenter Natasha Collins was found dead in January

The BBC said it accepted Speight's decision.

Joe Godwin, head of Children's Entertainment and executive producer of SMart, said: "The next series of SMart is just about to go into production and, given Mark's recent terrible loss, we completely understand his decision. Everyone at CBBC wishes him well."

Scroll down for more...

Mark Speight with Natasha Collins on the children's show See it, Saw it