(Cover) - EN Showbiz - Kristen Stewart might find it hard to keep the promises she has made to Robert Pattinson because she's "very ambitious", it has been claimed.

The Twilight actress is recently thought to have reunited with her co-star and boyfriend, following her affair with married film director Rupert Sanders.

Kristen is thought to have told Robert she'd do anything to rekindle their romance, but it's been suggested her work might come first.

"Kristen's telling Rob she'll take some time off to be with him, but she's very ambitious - if a great role comes up, she'll find it hard to refuse. At the moment, they're focused on Twilight and Rob can keep her in his sights, but after that it will be tough," an insider told Heat magazine.

Robert and Kristen will promote the last Twilight movie Breaking Dawn - Part 2 together soon. He is said to be concerned about how fans will react to them.

"He doesn't want to be seen as a pushover or get laughed at. Up until now he and Kristen haven't been on many dates," the source added. (C) Cover Media