The singer made the revelation during a recent interview with The Guardian.
Legend and Teigen met in 2007, when the model was cast as the love interest in the music video for his song "Stereo."
"We spent the whole day dancing together, grinding together," he said. "And, uh, we made a music video."
They became a couple and have been together for more than a decade other than, Legend told the publication, an attempted breakup that lasted only half an hour.