Christina Aguilera may be taking a season off from The Voice, but that doesn’t mean that she’s not still actively harassing co-coach Adam Levine.

 

These two have had quite the bumpy relationship. They started as frenemies and things turned sour on Season 2 of The Voice when Adam coached former Mouseketeer Tony Lucca. Xtina made some biting comments about her former Disney co-star, and they didn’t sit too well with Adam.

 

But in Season 3 we saw a sibling relationship develop between the coaches. They love giving each other a hard time, and that really showed yesterday when Christina tweeted to Adam on his birthday.

 

“Happy Birthday @adamlevine! I know you'll be whipping out tequila shots tonight. U turn 40 right? Hehe. U know I'll always bust your balls,” she tweeted.

 

Adam actually turned 34, but who’s counting?

 

We love that these two are still joking around even when the cameras aren’t rolling. Hopefully Xtina will be back for Season 5 of The Voice, which is set to air in fall 2013. Colombian pop star Shakira is taking over for Christina in Season 4, which premieres on March 25.

 

Do you think Christina and Adam are actually friends in real life? Tell us below!