I saw when it happened. It was a song called, "Girl You Know It's True". The line in the song went, "Girl, you know it's true! Ooh, ooh, ooh, I love you" But they got busted when the song kept repeating, "Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it...Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... Girl, you know it... etc. The whole time Milli and Vanilli stayed on stage and tried to play it off. It didn't work.
For the several months before, Arsenio Hall got really mad at them, and labled them frauds when the deal to have them on his then TV talk show went bust. The deal went bust when they refused to show proof they can sing live. Arsenio Hall did not want to feature musical acts who didn't/couldn't sing their own songs.