Underwood, 26, who announced her engagement on Dec. 21, talked about it for the first time in a holiday posting on her Web site: "I think you all know what Santa left under the tree for me this year ... a fiancé! Woo hoo! Little Ace is finally going to have a dad! We all couldn't be happier!!!"
The country singer and her Ottawa Senator fiancé, 29, met in October 2008 after being introduced by mutual friends.
Besides the rock, Underwood bragged about the other things she found under her Christmas tree, including "a pair of pink warm fuzzy socks to keep my tootsies nice and toasty" and lots of tasty chow.
"I ate so much on Christmas Eve that I thought I might actually get sick! But it was sooooo goooood!" she wrote on her Web site, reminding fans to "stop and reflect on the true meaning of Christmas."