Sebastian Sartor walks out of the Best Buy in Manhattan's Union Square Tuesday night empty-handed. "I just tried to buy the Pusha T album," he says. "I did a proper, thorough search. I went to the desk and [asked], 'You're sold out?'" He smiles. "That's awesome."

Sartor has a personal investment in Pusha's new My Name Is My Name, released Tuesday (October 8)—he's the producer behind the much-discussed album opener, "King Push," which made headlines back in August when Push told Vibe that it was produced by reclusive movie star Joaquin Phoenix. Sartor, 23, is decidedly not Joaquin Phoenix. Nor is he Lars Ulrich's son, which is what Pusha told Rap-Up the day after Phoenix released a statement to XXL saying he'd merely introduced a friend's son to Kanye's camp. As Push continued on his promotional tour, the real story behind "King Push" got murkier and murkier, with the only certainty being that Push didn't know the answer to the question everyone kept asking.

The real story is this: Sartor's father is an Italian artist, and his mother is actress Connie Nielsen. Nielsen starred opposite Phoenix and Russell Crowe in Gladiator in 2000 as Lucilla, the sister and love interest of Phoenix's Emperor Commodus. It was on that set that Nielsen—and Sartor—met and befriended Phoenix. Ulrich's name enters the picture because a few years later, he and Nielsen began dating and had a son in 2007.

So Push's versions came close. But how, exactly, did a young producer come to land a track on one of the most highly anticipated hip-hop albums of the year? Phoenix, while not involved in the production in any way, played middle man after meeting up with Sartor in L.A. earlier this year. "I've known Joaquin for a while, and we just kind of reconnected," Sartor says over a slice of pizza on University Place. "I played him some stuff—I just wanted to get feedback, I never expected it to go the way it went. I played him the track, and he said to me, 'I'm gonna play it for my friend.' It wasn't Kanye. But it was crazy."

Sartor has been producing tracks for about two years, starting out while he interned for Universal Music Group in London, before quitting a different job at the end of last summer to focus full time on music. The beat that became "King Push" was crafted at his windowless studio in L.A. around the beginning of the year and marked a turning point for him in his own production style. "I had gotten a new bank of patches, a new synth," he explains. "I was scrolling through, and I immediately got inspired by this sound I heard, and I tried to fuck around with some chords. And [I] just built [it] slow, step-by-step, really feeling it and trying to disconnect certain senses with really low light. It all started coming together and matching up in like three, four days, five days, I think. I made it my only focus—I wanted to make it dope. I wanted to change the way that I produce and the way that I paid attention."

A week after sending the track to Phoenix, Sartor got an e-mail out of the blue: Kanye wants your beat. At the time, the track existed as a file on his hard drive titled "Eerie Dark 2," a drive that he had forgotten in the studio while he was packing up and moving back to New York a few months ago. After Fed Ex-ing the studio keys to a friend, he recovered the track and sent the original stems to Yeezy's camp. "I was super worried about it at first," he says about sending over the individual stems. "I was like, man, this sounds weird... I was just hoping that it ended up on something really dope. I trusted so much." After that, all he could do was wait.