Clarkson, 30, accepted Blackstock's proposal Dec. 14. "I'm engaged!" she tweeted the following day. "I wanted y'all to know! Happiest night of my life last night! I am so lucky and am with the greatest man ever."
Clarkson shared a picture of her dazzling ring via WhoSay. "It's a yellow canary diamond with diamonds around it," she wrote in the caption. "Brandon designed it with Johnathon Arndt! They did an amazing job! I can't wait to make Brandon's ring with Johnathon as well!" (Arndt also designed fellow American Idol winner Carrie Underwood's ring.)
This will be the American Idol winner's first trip down the aisle. Blackstock, who's the son of Clarkson's longtime manager Narvel Blackstock, and the stepson of Reba McEntire, has two children from a previous marriage. The two currently live together in Nashville.
While chatting with DeGeneres last month, the "Catch My Breath" singer joked that her beau would have to "put it a ring at some point."