Credit: Ian Gavan/Getty Images

Bounty Hunter costars Jennifer Aniston and Gerard Butler haven't fessed up to any romantic involvement in real life, but their director says they're awfully good at faking it.

"When you have that chemistry [between actors] you're like 'Thank God!' because they're having fun on day 45 and day 65 and they're still flirting," director Andy Tennant told at Thursday's London premiere for the movie.

"Gerry likes to have fun, Jen likes to have fun, they don't take themselves seriously --- which is a big mistake people assume with Jennifer, but she's a riot!" Tennant told Us. "So we went out [during filming] and had a good time."

What of talk about Aniston-Butler hookups? Aniston joked to one reporter that she blames Butler. "He starts those rumors! It's his fault!" she said on the red carpet, laughing.

"Gerry is the best," she cooed. "He's funny and handsome. Nice combo!"

"We have a natural chemistry," Butler admitted to reporters. "You can see it in our magazine shoot and the film, we have a great time together."

In the film, the actors play ex-lovers reunited for a crime caper. One GMTV interviewer asked Aniston -- ex-wife of Brad Pitt -- if exes could get back together in real life.

"Absolutely!" Aniston replied. "Sometimes you meet each other a time in your lives and you're not necessarily're not fully formed to have maturity it takes to be in a relationship...It's not all black and white."