Will Ferrell has branded Kristen Stewart a ''trampire'' for cheating on Robert Pattinson.

The 'Everything Must Go' star appeared on TV talk show 'Conan' and 'broke down' over the actress' split from Robert Pattinson - who she first me on the set of vampire franchise 'The Twilight Saga'.

When host Conan O'Brien asked a forlorn Will what was wrong with him the comedy actor jokingly opened his heart over his feelings about Kristen's affair with her 'Snow White and the Huntsman' director Rupert Sanders.

In what appeared to be a spoof of super-fan Nutty Madam's tearful video post about Kristen's cheating, he said: ''I don't know if you follow the news at all, but there's this actress, Kristen Stewart and she goes by K-Stew, and she had a boyfriend Robert Pattinson - he's R-Patz - and she cheated on him. And they've broken up, they're not going to get back together, ever. What they had was so special Conan, you don't even know what they had, they were in love and she just threw it all away.''

Pretending to hold back tears, he added: ''I don't know if there was anything I could have done to prevent this. I don't know what it means to the 'Twilight' franchise. It's not going to be fine ever! (shouting) It's never going to be fine. She is a trampire, that's what she is.''

The audience cheered loudly as he called Kristen a ''trampire''.

The 22-year-old starlet and Robert, 26, have both moved out of their Los Angeles home and the heartbroken actor is staying at his friend Reese Witherspoon's holiday home in California as he tries to get over his heartbreak.