The former Spice Girl sent fans wild when she interrupted her scripted scene to begin her rap from the band's 1996 debut single Wannabe during her final turn as Roxie Hart at the Ambassador Theatre in New York.
In a video Mel posted on Instagram, she can be seen walking around the stage and saying in an American accent, "I'm going to tell you something..." before launching into her British voice to sing "so here's the story from A to Z" from Wannabe. She laughs as the audience scream before she says, "back to my character... I'm gonna tell you something, as Roxie."
In the caption, she wrote, "Here is a snippet of me last night doing my last show In @chicagomusical playing Roxie heart (sic) breaking character busting out some spice power haha #nyc #broadwaybaby."
To mark the end of her run, she also shared a video of her breaking character for a second time to giggle with actress Amra-Faye Wright, who plays Velma Kelly, while they are singing and dancing the show's finale number. In the caption, she wrote, "Giggle fit, you made me do it @amrafaye."
She also posted a throwback picture of herself back in her Scary Spice days walking into the MTV Europe Music Awards and making a funny face and throwing up the peace sign. She wrote, "Me walking off broadway last night at my last show."
The 41-year-old has been frequently asked about the Spice Girls reunion and she still hopes to perform with bandmates Emma Bunton and Geri Horner to mark their 20th anniversary.
"I'm trying everyone, I'm trying. I'm so down to make this happen, you have no idea," she said on Australian TV show Sunrise. "It's just a case of getting everybody else on the same page.
Mel C and Victoria Beckham will not be taking part.