In 2012, Nicole even admitted to singing 95% of the group's vocals.
Things all came to a head at the 2006 "Fashion Rocks" concert when Melody randomly appeared onstage and in a very random moment started wailing.
Nicole was pissed and visibly shaken.
It would give us one of the most iconic and awkward 30 seconds in music history. Watch it here:
Years later, Melody isn't part of the Pussycat Dolls reunion, and now we know one of the reasons why.
She told the Mirror UK: “I was a singer, not a trained dancer, but wasn’t allowed to sing and was told I couldn’t dance."
She also said that she was never mad at Nicole.
She said: “People would assume that I was so mad at Nicole because she sang and I didn’t. Well, no. That was her dream and it was coming true for her. I just wanted it for myself, too. I wanted the best for everyone. I’m a phenomenal vocalist; you just never heard it. But it wasn’t Nicole’s fault."
So there you have it: There's no bad blood between the girls.
Now let's all focus on how amazing their X Factor UK comeback performance was and replay that American Music Awards clip over and over until we die.