Looks like Ed Sheeran spilled a few of the beans and tells a story he heard through the grapevine. In a recent interview he tells how he heard about Eminem wanting Kendrick Lamar on a track, but he wanted to make sure no ghost writers were involved.
(start listening around 8min mark)
“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.”
Don’t test my guy anymore lol. He passed them all!