Kanye West** made quite the declaration to a crowd of 5,000 when referring to girlfriend Kim Kardashian as his "baby mama" at a Sunday concert, and no one was more surprised to hear his announcement than Kardashian herself.

"[Kanye's announcement] was a surprise!" a source close to Kardashian, 32, tells Us Weekly just hours after West made the big reveal during a concert at Atlantic City's Revel Resort. At just three months pregnant, Kardashian -- in the audience at Sunday's show -- was "deciding when to announce and if she could hide it. She's not big or showing at all."

On Monday morning, the pregnant reality star took to her blog to elaborate on West's weekend announcement. "It's true!! Kanye and I are expecting a baby. We feel so blessed and lucky and wish that in addition to both of our families, his mom and my dad could be here to celebrate this special time with us," the Kourtney & Kim Take Miami star wrote on her Celebuzz blog early Dec. 31, referring to her late father Robert Kardashian, Sr. -- who died of esophageal cancer in 2003 -- and West's mother, Donda, who passed away four years later.

As she says goodbye to 2012 at a bash in Las Vegas, Kardashian can't wait to see what the new year has in store. "Looking forward to great new beginnings in 2013 and to starting a family. Happy New Year!" Kardashian blogged.

Could 2013 include a proposal? Though Kardashian is still legally married to Kris Humphries**, a source close to dad-to-be West tells Us the rapper intends to pop the question once her divorce is settled. Says a pal: "He's told friends and family he was gonna [marry] her since the day they met."

This article originally appeared on Usmagazine.com: Kanye West's Pregnancy Reveal at Concert Was a Surprise to Kim Kardashian