The rapper and Gaga worked on Partynauseous together in 2012, but the track was shelved after the Poker Face hitmaker fell out with members of Lamar's production team over creative differences.
She briefly addressed the drama in 2012, when she admitted, "This situation with Partynausous is confusing".
She added, "When I collaborate with an artist I work solely with them, not with their camps or management. It's purely organic and creative. I love Kendrick dearly as a friend, but was not willing to compromise musically to the changes his team was making to my music..."
However, on Thursday (21May15), fans finally got a chance to hear the track when it leaked online.
Lamar and Gaga have not commented on the apparently unauthorised release.