An excited Clarkson announced the happy news to fans via Twitter.com last week (15Dec12), but The Voice judge insists he played a big part in helping the pair take a step towards the altar.
Shelton tells Hollyscoop.com, "I told Brandon, 'Man, you need to grow up and figure out that you need to marry this girl.'
"I am going on the record saying, 'I will do the music at the wedding or whatever you want to do, I'll be that guy. I will play for four hours if I have to, cause (sic) you need to get your head out of your a** and ask that girl to marry you.'"
Shelton isn't the only artist offering his services for the couple's reception - Blackstock's step-mum, Reba MCEntire, is also keen to perform at the wedding party.
In a Twitter exchange with the bride-to-be on Wednesday (19Dec12), MCEntire asked, "speaking of the engagement, since you are going to be my daughter-in-law, I'm singing at the wedding, right??", prompting a cheeky Clarkson to reply, "Obviously! My request is 'Let's Get It On' by Al Green. That's not awkward, right?"
Clarkson began dating Blackstock earlier this year (12).