TLC's 1995 single "Waterfalls" was the R&B trio's biggest hit, spending seven weeks at No. 1 on the Billboard Hot 100. But it was far more than just another pop hit: The track told a cautionary tale of HIV and AIDS, and its video depicted a man who didn't wear a condom with his girlfriend and later watched his body degenerate in the mirror. "His health is fading and he doesn't know why," the trio sang. "Three letters took him to his final resting place."

"The video spoke for a whole epidemic," says T-Boz, who with Chilli are the remaining TLC members following Lisa "Left Eye" Lopes' death in 2002.

T-Boz adds, "We used to have so many patients come up and say, 'Thanks for being our voice and getting the message out there to let people know how easily this is contracted.'"

While the trio's iconic voices are unmistakable on the track, fans may be surprised to learn there was yet another superstar singing on the track: Cee Lo Green!

"He was chilling in the studio, so I was like 'Hey, you sing good, why don't you [sing backup]?" T-Boz recalls of The Voice coach. "He was in Goodie Mob, we grew up together, we go way back. He did and it was amazing! I love his voice. Then, everybody knew him as a rapper. Now, the world knows him as a singer, but he was like that years ago."

Watch the full interview above for more on "Waterfalls," including details about Left Eye's verse. Then go back in time with the original "Waterfalls" music video below.