Lady Gaga tells MTV that she penned her new duet with Cher, 'The Greatest Thing,' years ago but never found the proper home for it until now.

"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 says. "I always write these concept records, and it just didn't fit in. But it's always been this big, massive, beautiful hit record and everyone always says, 'Why don't you put that on your album?' I said, 'I don't know, it just doesn't fit with everything else.'"

"Cher heard the song and loved it and wanted to do it together," Gaga adds. "And I said, 'F--- yeah, it's Cher!'" 'The Greatest Thing' is set for a September release, with Cher's 26th album to follow at some point thereafter.

Gaga had never met Cher until last year's VMAs, when the ageless diva presented the meat dress-wearing Gaga with the award for Video of the Year for 'Bad Romance.' Gaga asked Cher, a vegetarian, to hold her meat purse while she made her acceptance speech.

"I don't think she realized I was handing her meat," Gaga says. "She was like, 'No problem, I'll hold your purse.' And then she just sort of had a steak in her hand. I was like, 'Thanks, b----h!'"

Gaga will be back at this year's VMAs, where she is a multiple nominee, and will open the show with a performance.

Watch Lady Gaga Talk About 'The Greatest Thing'