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.

"You know when time just blends in together and you have no fucking clue what happened?" Sartor says in his British accent that he picked up in his six years living in London. "I don't even know, time just disappeared. And everything just blended in with moving [to New York], and it was just like, whoa, what the fuck?"

After sending off the stems, Sartor was met with radio silence, not knowing what would happen to his beat, how Kanye's team might chop it up or whether it would ever be released anywhere at all. And then Pusha gave his interview with Vibe. "When I turned in [the album] in June, [Kanye] gave me probably two or three new beats,” said Push at the time. “One of those beats was from Joaquin Phoenix, and it’s probably gonna be...I want it to be the intro to my album.”

"I did hear that, but I didn't know what they did with it," Sartor says; it was the first confirmation he had that his music might be surfacing. "Maybe they took, like, the intro, maybe they took a sound, a small part... I didn't even know how someone could rap over it. [Laughs] And then, it was amazing."

It turns out Kanye barely touched the track, if at all—the full instrumental Sartor provided them became the full backbone of "King Push." But Sartor still didn't know that—he was denied from Pusha's listening party in New York, having been left off the list, and couldn't hear the album. "The first time I heard it was when I didn't get to go to the listening party," he says. "I wanted in so bad that I think I sat on Instagram and just typed in hashtags that it could have been. And somebody had taken a video of a 10-second snippet of the end of the track. I was like, 'It's on the fucking record!'"

He still hadn't heard the whole track or found out what Kanye had done to it. That didn't come until Push dropped the music video for "King Push," another unexpected move that put the song, and it's eerie, dark tones, back in the headlines. "The first time I heard the full thing was the music video, and I think I listened to it like 100 times on repeat," he says. "It was so dope, I couldn't even...I think I was just joyous. It was even better than getting the e-mail."

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Sartor joins the likes of Wondagurl—who placed a beat on Jay Z's Magna Carta...Holy Grail—and Young Chop—whose beat was flipped by Kanye for his "I Don't Like" remix which launched Chief Keef into the stratosphere—among young producers who have been mined for high-profile beats. But this isn't his endgame: the day the album came out, Sartor was in the studio by 6 a.m., working on what's next. "I bought the album on iTunes, but I wanted a physical thing," he says, explaining his trip to Best Buy. "I wanted to touch the album. [Laughs] I don't believe it until I see it. It's been cool to see such a response, and I hope you guys get to hear more of my stuff."

The Italian-born, New York City-raised Sartor moved back to NYC three months ago, and since then he's been working with rappers he's met around the city, as well as friends he hung with in London when he was first starting out behind the boards. His initial hesitation about doing interviews—he hasn't spoken to many people about the track, preferring to let the music speak for itself—has given way to a desire for more work, more beats, more tracks. "[I'm] just trying to get my name out. I'm hungry man, I wanna make music," he says. "I've been in the studio working and trying to make things happen. I want to make beats that I'm always proud about. That could be maybe timeless one day."

He's been working all day, but since the album has finally come out, he allows himself a moment to reflect on the track. "It's next level, man," he says, smiling again. "It's nuts." —Dan Rys (@danrys)