RuPaul explains how Lady Gaga asked to appear on 'Drag Race'

— -- "RuPaul's Drag Race" kicks off its ninth season Friday night with a very special guest judge: Lady Gaga.

This is the first time the singer has appeared on the reality TV show.

According to the host, Gaga has long been a fan of the show.

"She attributes a lot of her [joie de vivre] to her life with [drag] queens in clubs," he told ABC News. "So she tweeted me maybe three years ago and said, 'Ru, why can’t I be on the show?' And I said, 'Are you kidding??'"

However, it's taken this long for Gaga to fit the appearance into her busy calendar.

"Doing these kinds of shows, the hardest part is scheduling people," he said. "So finally, we got her on the season opener and it is a blast. You’re not ready for this!"

This won't be the first time that Gaga and RuPaul have teamed up on TV, though -- he was a guest on Gaga's ABC holiday special with the Muppets a few years ago.

"She’s an amazing person and a really loving person," he said. "And I’m always surprised when I see these people because she’s a child! You know, when you strip down the makeup, it’s like, 'Oh my God!'"

Other judges on this season of the VH1 show, which premieres at 8 p.m. ET, include Meghan Trainor, The B-52s, Kesha, Lisa Kudrow, Jennie Garth, Tori Spelling and many others.