“Do I wear a Team Jacob shirt or a Team Edward shirt?,” jokes the singer/songwriter. “You know what? I’m Team Bella all day.”

Co-written and produced with the Smeezingtons (Mars, Philip Lawrence and Ari Levine), Mars had been working on what would become “It Will Rain” on the road before getting the call to contribute to the soundtrack. He says “after seeing the movie, I thought that it would be a perfect fit.”

“It Will Rain” will be released globally on Sept. 27, for sale exclusively via iTunes (save for in the U.K., which will get the song in early November). On Sept. 26, the full tracklist for the Summit/Chop Shop/Atlantic album, due Nov. 8, will be revealed.

Mars says that “the ‘Twilight’ movies for me (are) a love story. But it’s a dark love story. And I think the best way to describe the song is: it’s the darker side of love. I think that pretty much sums it up.”

“It Will Rain” “started off with me and the guitar,” Mars says, “and I just had this melody in my head and basically laid it down after I saw the film.”

Lucky Mars got to see “most of the movie” so he “could catch the vibe and feel where they were going with it.” But, he doesn’t know (or won’t divulge) where the song will be heard in the film itself. “I have no idea! As long as it’s not after the credits. I hope it’s in a good (scene)!”

Mars says that “It Will Rain” is intended just for the “Twilight Saga: Breaking Dawn” soundtrack and not for his own on-the-horizon second album. “I personally think if I did this for the ‘Twilight’ soundtrack, then this is for the ‘Twilight’ soundtrack,” he says. “This is not for my album.”

His first album, “Doo-Wops & Hooligans,” debuted and peaked at No. 3 on the Billboard 200 in 2010 and has sold 1.3 million copies in the U.S. according to Nielsen SoundScan. The first two “Twilight” soundtracks hit No. 1 on the Billboard 200, while the third, “Eclipse,” reached No. 2 last year. Collectively, they have shifted 4.5 million in the U.S.

Could we possibly see a collaboration in the future between Mars and “Twilight” star Robert Pattinson? The latter has been in the news after rumors started swirling about how he was working on his own album.(Turns out, he’s not “working on an album right now.”)

Don’t rule it out: “Why not?,” Mars says. “I’m down for anyone that wants to work and thinks I can contribute.”

Bruno Mars is making it “Rain” for the newest “Twilight Saga” film installment.

The singer/songwriter is the first confirmed artist for “The Twilight Saga: Breaking Dawn – Part 1 Original Motion Picture Soundtrack,” with the exclusive new track “It Will Rain.” The song will be revealed and up for sale on Sept. 27, same day as the soundtrack pre-sale, and the day after another massive unveiling.

The entire tracklist for the “Breaking Dawn” set will become available on the “Twilight Saga” Facebook page and Twitter on Monday (Sept. 26).

Mars made the announcement on his own website, with the single artwork.

Just this week, rumors began to swirl that the film’s co-star Robert Pattinson would be contributing music to the soundtrack. As we previously surmised, Muse may contribute again, considering the British band contributed tracks to all of the other sets.

And if Summit/Chop Shop/Atlantic want to keep a trend going, every song on “Breaking Dawn – Part 1″ will be an exclusive contribution, meaning they’re songs or remixes unavailable anywhere else.

“The Twilight Saga: Breaking Dawn – Part 1 Original Motion Picture Soundtrack” will be released on Nov. 8.