Two of pop's biggest divas, Lady Gaga and Cher, are teaming up for a highly anticipated collaboration, fittingly titled "The Greatest Thing." Late last week Cher confirmed via Twitter that the song will be out in September, but few details have been revealed about the Gaga-penned track.So when MTV News caught up with the VMA-nominated Mother Monster herself last week, we asked her to dish about the track. It turns out that "The Greatest Thing" was a song she had been holding onto for some time."I wrote that song a long time ago, and I've never put it on one of my own albums for, really, no particular reason," Gaga told us. "I always write these concept records, and it just didn't fit in. But it's always been, like, this big, massive, beautiful hit record and everyone always says, 'Why don't you put that on your album?' And I said, 'I don't know, it just doesn't fit with everything else.' "The song was, however, a good fit for Cher's new record and it will reportedly be the lead single off of her yet-untitled 26th studio album."Cher heard the song and loved it and wanted to do it together," Gaga added. "And I said, 'F--- yeah, it's Cher!' "Of course, this collaboration may never have happened if it were not for last year's VMA show, where Cher handed Gaga her Video of the Year Moonman for "Bad Romance." Lady Gaga graced the stage in her infamous meat dress, making a memorable first impression on Cher — and the rest of the world."I don't think she realized I was handing her meat," Gaga recalled.So what was Cher's response to Gaga asking her to hold her meat purse?"She was like, 'No problem, I'll hold your purse.' And then she just sort of had a steak in her hand, and was like, 'Thanks, bitch!' " the "Born This Way" singer joked.Gaga is gearing up to create more memorable moments at the 2011 Video Music Awards. She'll open the big show with a performance on Sunday night.The 28th annual MTV Video Music Awards will air live Sunday, August 28, from the Nokia Theatre in Los Angeles at 9 p.m. ET/PT, following the Selena Gomez-hosted pre-show at 8. See the list of nominees, revisit last year's highlights and vote for Best New Artist by visiting VMA.MTV.com.