Robert Pattinson and Kristen Stewart can only appear together at "Twilight' themed" red carpet events.

The couple - who also star alongside each other in the vampire franchise - reportedly have a clause written into their contracts preventing them appearing at any other red carpet event together, explaining why Robert was alone at the premiere of Paul McCartney's video to his latest song 'My Valentine' in Los Angeles last week.

A source told Hollywoodlife.com: "One [reason Robert was on his own] was he didn't want to make it the Kristen and Rob show and take away from the actual event.

"They also have a clause in their Twilight contracts that they can only appear together at a Twilight themed red carpet together. Twilight kind of owns some of their appearances they do together until [final 'Twilight' film] 'Breaking Dawn: Part 2' is one hundred per cent completed."

Meanwhile, it has been confirmed filming on 'Breaking Dawn: Part 2' isn't over yet and both Robert, who plays lead vampire Edward Cullen, and Kristen, who portrays his wife, Bella Swan, have been recalled to Canada to shoot some "technical" scenes for the film.

Writing on Facebook, director Bill Condon said: "We're not shooting any new scenes or dialogue, just some technical work with some of our cast and stunt actors.

"I am really looking forward to being back on set with some of the friends I've made on my 'Twilight' journey, like the great Guillermo Navarro, our cinematographer, and his crew. And yes, Rob and Kristen will be there too."

'Breaking Dawn: Part 2' is set to be in cinemas this November.