The rapper reportedly spilled the beans during a concert in Atlantic City, N.J. Sunday night, whenhe paused during his set to ask the crowd to "stop the music and make noise for my baby mama," referring to Kardashian, who was in the audience.
The couple was first publicly linked this past spring, though Kardashian is still legally married to NBA player Kris Humphries. She filed for divorce from him in late 2011. Humphries is expecting his own child, with ex-girlfriend Myla Sinana.
The Kardashian family seems overjoyed at the news. Kim's sister, X Factor host Khloe Kardahian Odom, tweeted: "KIMYE!" followed by, "Keeping secrets is hard with so many family members! Especially when you are so freaking excited! Love is everything!"