He'd decided not to attend the ceremony in 2003, leaving his collaborator Luis Resto to accept the award from legendary actress-singer Barbra Streisand.
In an interview with variety.com, Eminem, whose real name is Marshall Mathers, opened up about how his Sunday night's performance came together.
"I kinda figured maybe since I didn't get a chance to do it at the time, maybe it would be cool. Back then, I never even thought that I had a chance to win, and we had just performed 'Lose yourself' on the Grammys with the Roots a couple of weeks before the Oscars, so we didn't think it was a good idea. And also, back at that time, the younger me didn't really feel like a show like that would understand me," said the rapper.
"But then when I found out I won, 'That's crazy!' That to me shows how authentic and real that award is -- when you don't show up and you still win. That makes it very real to me," he added.
He doesn't know if he was disappointed about missing the ceremony back then, he was "blown back by the fact that I won".
"I don't even think I understood back then that you could get an Oscar for a song, and I remember being kinda confused about why I was even up for one, because as a kid with the Oscars, it was like a vacuum," said Eminem.
At the time, some reports said he didn't perform because the Oscars wanted him to do a censored version of the song.
"Oh no, that wasn't the case at all, because there's not even that many cuss words in it - there's only a couple. That's not true at all," he clarified.
He enjoyed being at Oscars this year. "Absolutely. I got to hug Salma Hayek," he shared.