While Law & Order: Special Victims Unit has had plenty of familiar guest stars, the latest was a surprise even for Mariska Hargitay.

After appearing in the Season 27 episode ‘Gimmick’ as a professional fighter, Melissa McCarthy shared a behind-the-scenes video of herself dressed in disguise so she could surprise Hargitay on set with her guest appearance.

“Sometimes you just have to show up to give a proper ATTA GIRL to a total (ultimate) boss lady,” she captioned a video. “Turns out it is VERY hard trying to keep secrets from @therealmariskahargitay on her set but we managed to pull it off and in a world where things are heavy and dark but this day was PURE JOY.”

McCarthy added, “Mariska, you are the real deal. Sorry everyone lied to you, hope it was worth it (this surprise was six years in the making people)!!! PS LOOK MA I FINALLY MADE IT ON LAW & ORDER!!!!!”

Hargitay shared a behind-the-scenes selfie with McCarthy. “SURPRISE!!!! #MELISKA mind blown and still doing the happy dance!” she wrote.

With her appearance on the show, McCarthy joins the ranks of past guest stars, including Patricia Arquette, Billy Porter, Patti LuPone, J.K. Simmons, Viola Davis, Brooke Shields, Leslie Odom Jr. and more.

Law & Order: SVU continues its record-breaking streak as TV’s longest-running primetime live-action series after it was renewed for Season 28 this month.