Blake Shelton Told Kelly Clarkson's Fiancé: 'You Need to Marry This Girl!'

By Dahvi Shira

12/19/2012 at 05:00 PM EST

Kelly Clarkson has someone she owes an extra special thank-you to this holiday season.

The Grammy-nominated pop star, 30, wouldn't necessarily be closing out 2012 as an engaged woman if it weren't for Blake Shelton.

"I told Brandon [Blackstock], 'Man, you need to grow up and figure out that you need to marry this girl,'" Shelton, 36, who is managed by Clarkson's fiancé, told Hollyscoop. "You need to get your head out of your ass and ask that girl to marry you."

PHOTO: See Kelly Clarkson's Huge Engagement Ring

The Voice coach was so adamant about the proposal that he even offered up quite the personalized present.

"I am going on the record saying I will do the music at the wedding or whatever [they] want to do," Shelton said. "I'll be that guy. I will play for four hours if I have to."

Clarkson, who announced her engagement on Saturday via Twitter, calls herself "so lucky [to be] with the greatest man ever."

"I'm so glad he did [it],” adds Shelton. "He is one hardheaded dude – and she's the best thing to happen to him."