Eminem was so convinced that Kendrick Lamar could be using a ghostwriter that he made the rapper write his verse for “Love Game,” a track from the 2013 album The Marshall Mathers LP 2, without anyone else in the room. That’s according to Ed Sheeran, who heard the story from Rick Rubin, executive producer of MMLPII, and relayed the tale on The Zach Sang Show. Hear the story above at the 8-minute mark, which was spotted by HotNewHipHop.

“Eminem heard that Kendrick Lamar was the best rapper and he invited him to the studio to get him on a song,” Sheeran says in the interview. “He arrived and Kendrick came with all his mates and Eminem said, ‘I just want you in the studio, just you on your own and then my engineer is gonna come in and then record you doing it, but your mates aren’t allowed in.

“Kendrick did it, wrote a sick verse, and then everyone came in to listen to it. Eminem said that he did it to test Kendrick because he thought he had a ghostwriter. He then realized that he didn’t then claimed [Kendrick] was the best.”

To his credit, Kendrick suspected what was going on. In 2014, he discussed the song’s recording process during a radio interview. “He brought me out to Detroit, I had a show, and he brought me to the studio to do a hook… I go in, do the hook, and he’s like ‘I like the hook.’ Then I’m like, ‘Alright, cool, I’m finna dip,’ then he says ‘Think you could do a verse?’… The thing with Em which was crazy to me is he kicks everybody out of the studio… I took it as him kicking everybody out to see if it’s really you writing those raps that you’re writing.”

Last year, Eminem released “Campaign Speech,” a new nearly-8 minute track that garnered a bunch of strong opinions. The rapper is currently working on a new album.