If you were lukewarm on Kendrick Lamar’s "i," that may be because you didn't yet have quite the full story.

It turns out the track has a complimentary piece, called "u," which will be included on K. Dot's upcoming To Pimp A Butterfly album.

"That was one of the hardest songs I had to write," the 27-year-old told Rolling Stone in a new cover story. "There's some very dark moments in there. All my insecurities and selfishness and letdowns. That sh-t is depressing as a motherf--ker. But it helps, though. It helps."

Kendrick, who is on the cover of the magazine's most recent issue, also gave them a preview of some of the other music on the new album: "Mortal Man" was reportedly inspired by a trip he took to South Africa last year, while the story calls "King Kunta" a "stomping blast of James Brown funk."

There are a bunch of other cool and fascinating tidbits in the story, which is on newsstands now. For one, Kendrick says he started keeping a diary the week good kid, m.A.A.d city was released in 2012: "I didn't want to forget how I was feeling when my album dropped, or when I went back to Compton."

He also talks about battling self-doubt, goes into detail about some of the violence he witnessed growing up as well as run-ins with police, plus we hear from both of his parents (in a different way than we did on the album).

As for To Pimp A Butterfly, Dot calls it "fearful, honest and unapologetic."

Oh, and that title? "Just putting the word pimp next to butterfly...It's a trip," he explained, saying he could possibly be "both" of the characters mentioned in the title. "That's something that will be a phrase forever. It'll be taught in college courses -- I truly believe that."

Class will be in session starting Mar. 23, when the album drops.

Watch Kendrick explain why he wrote "i" and some of the issue surrounding it below.