Sporty Spice Totally Crashed Little Mix's Video Party: Find Out How

Not even Little Mix knew Mel C was going to be on the set for 'Word Up!'

Little Mix has traded in their high heels for tennis shoes in the group's video for their new single "Word Up!" During the gym-themed clip, the foursomes are found pumping iron, sweating it out in a spin class and dancing with former Spice Girl Mel C, a.k.a. Sporty Spice, who the ladies said was a huge surprise for them on set.

"We didn't even know she was going to be there. Literally, we were filming and then she come running out," Jesi from the group told MTV News when asked how Sporty Spice's cameo came to be. "It was so weird though, I was thinking, God, I was such a massive fan."

But it wasn't just Little Mix who were starstruck during the making of the music video. Apparently Mel C's 5-year-old daughter, Scarlet Starr, is an equal opportunity listener when it comes to girl groups.

"The fact that she comes over with her daughter and was like, 'My daughter is such a massive fan — Can we get a picture or something?' " bandmate Perrie squealed with excitement. "She doesn't hold back either, she just goes for it. She's amazing."

The song serves as an official single for Sport Relief, an organization that unites the worlds of sports and entertainment to raise funds for charitable causes in both the U.K. and other countries around the world. Every purchase of "Word Up!" is helps Sport Relief meet their goal of creating jobs and better chances for 150,000 of the poorest people in sub-Saharan Africa, giving them the means to lift themselves, their families and their communities out of poverty.