Downey and Galifianakis Feuding Over Gibson?

Sources say things are icy between Due Date costars Robert and Zach since Mel lost his The Hangover 2 cameo

Mel Gibson has three friends in Hollywood: Whoopi Goldberg, Jodie Foster—and Robert Downey Jr.!

After director Todd Phillips' failed to bring Gibson on for The Hangover 2, we're hearing RDJ wasn't too thrilled with his Due Date costar Zach Galifianakis.

Here's why:

Robert has told Parade magazine it was Mel who taught him about second chances, casting Downey in Singing Detectives, his first flick fresh from jail, even though an insurance company wouldn't cover it.

So, RDJ thought it was time to return the favor.

He has the same rep as Gibson, and obviously got close with Todd during the filming of their hilar flick Due Date, and was very involved in getting Mel's name into the mix.

But the entire Hangover cast was über-pissed when Phillips sprang the Gibson cameo on them. So ticked off, that sources on the way secretive Hangover set confirm there were a lot of threats made by the stars of the sequel if Mel came onboard, with Zach on the front lines (can ya blame him?).

Apparently, tensions have been running high between Zach and Robert during the promotion of Due Date.

(Reps for both RDJ and Z.G. declined to comment.)

We're told from knowledgeable sources that Downey thought Mel really deserved another chance—and that he's subsequently been "pissy" with Zach, since he had a big part in getting Gibson axed.

The two did pose together at the end of the carpet at the Due Date premiere in L.A. last night after being asked, but they weren't exactly as buddy-buddy as usual.

Todd skipped most press because he didn't want to answer Mel questions, which was a big topic of convo on the carpet.

Ken Jeong said he wasn't allowed to say anything about Gibson-gate, while RDJ still defend him when asked.

Do you guys think Mel deserved another shot?

We're so with the Hangover guys on this one. What, is Robert forgetting that Gibson hates oh, I don't know, just gays, women, Jews, African-Americans, millions of Catholics, just to name of few?

—Additional Reporting by Martin Haro