The rapper opened up about working with Swift in an interview with Howard Stern on Tuesday, revealing that his decision to collaborate on "Bad Blood" didn't come lightly.
"One hundred percent," he answered when asked how much thought goes into which artists he lends his voice to. "You gotta have a great business mind, integrity and a great team, and the No. 1 thing we talk about is how does the music sound?"
"I'm a hip-hop artist, so how far in the pop world is the sound? So the first thing is, let's hear the music," he added, noting that he joined Swift in the studio and immediately recorded his part on the song. "The vibe was right. It didn't take too many takes. We locked in on the chemistry."
“I played him a record on there called ‘Complexion,'” he revealed. “It was just one of my favorite moments, he liked the record.”
According to the rapper, however, the potential collaboration slipped his mind amid all the activity. He was invited to Prince's estate for the day the late singer had an event planned, and ended up joining him on stage.
"It’s one of those things where, it’s so much going on in the moment, man," Lamar said. "I did a show with him that day, I didn’t even know I was coming out on stage. The studio was next door where I just played him the song. We were running back and forth.”
"It’s a surreal moment because this is one of the people I idolized," he added.
Hear more from Lamar's interview with Stern below: