The couple has been dating for about a month.
"Hi dolls," E! News reported Kardashian wrote on her Celebuzz blog Tuesday. "I'm thrilled to finally be able to tell you that the news is true... Lamar and I are getting married on Sunday!!! I couldn't be happier and I'm so excited that I can finally share the news with all of you.
"Your well wishes have meant the world to me and I am truly so blessed to have such amazing fans, family and friends during this incredible time in my life."