The `Since You`ve Been Gone` singer has announced she will wed 35-year-old talent manager Brandon Blackstock, who popped the question on 14.12.12 after nine months of dating.
The 30-year-old star - who shot to fame after winning `American Idol` in 2002 - shared her joy with her fans on Twitter, writing: "I`m engaged!!!! I wanted y`all to know!! Happiest night of my life last! I am so lucky and am with the greatest man ever."
Kelly recently expressed her hopes that the couple would tie the knot even though they weren`t yet engaged.
Last month, she said: "We are totally going to get married. We love each other. We are totally going to get married one day.
"I mean, he`s got to put a ring on at some point. But I`ll wait it out."
Asked if she has thought about the kind of wedding she wants to have, the `Stronger` singer said: "Honestly I`ve never been the girl to plan a wedding. We will totally, probably elope."
Kelly previously called their relationship her "best accomplishment" after years of being unlucky in love.
She said: "I completely fell in love. I did! Welcome to Cheeseville! I don`t know. Your priorities kind of shift and you become happier and all that stuff. It`s probably my best accomplishment because I think, for me, especially, I just didn`t think it would happen."