Is Zach causing trouble for Rachel and Adam?

Is one of Hollywood’s cutest young couples on the verge of a break up? Star magazine is reporting that Adam Brody and Rachel Bilson, of “The OC,� are having some trouble in paradise and that Bilson’s The Last Kiss co-star, Zach Braff may be part of the problem.

An insider told Star that even though it “looked like [Rachel and Adam] were on their way to getting engaged just a little while back,� they are now “going through a really difficult period right now.� Seeming to back up the story is the fact that the couple, who used to be photographed together quite regularly, have not been seen together in some time..

The source for Star claims that Zach might be a sore spot between the sparring lovers. He and Rachel became close while filming The Last Kiss and now “Zach calls Rachel a lot and they talk on the phone like girlfriends,� reports the insider. "But what really eats away at Adam is when Rachel starts talking about how mature Zach is. No guy appreciates his girlfriend comparing him to another guy.�

This isn’t the first time Braff has been rumored to be the third wheel in Bilson’s relationship with Brody. About a year ago the Last Kiss co-stars were linked when they were seen getting cozy at LA hotspot the Dime