Nick Carter Warns Brother Aaron: I'll Sue If You Lie About Me in Public

Nick Carter is not happy with his brother Aaron for publicly discussing details about him and their family business, so he sent a strongly worded legal letter warning his bro to zip it up or else.

The Blast has learned the letter spells out very clearly that if Aaron talks about the Backstreet Boys star he will have serious legal issues. Our sources say Nick loves his brother and really wants him to get help, and is willing to do anything for him to get healthy .

The problem is, after Nick showed his brother a little tough love by telling him he would only help financially and with his career if he got cleaned up and went to rehab. We are told Aaron responded by lashing out and spreading lies about Nick.

The public disclosure of false information forced Nick to have his lawyers draft the letter and fire it off. The letter, which was sent a few weeks ago, warns Aaron to not spread false information about the Backstreet Boy.

The legal threat seemed to work, Aaron has stopped publicly talked about his family in detail and we're told a reality show he was about to sign on to has been shelved for the time being.

We're told even though Nick sent the letter, he is still hoping his brother will get help and they can patch up their relationship. Nick knows his brother is in a bad place, and would do anything to help him pull through.

Aaron's rep claims he checked into rehab Friday.

The Blast first reported authorities rushed to the singer's home after they received multiple 911 calls that Aaron was suicidal and had been allegedly inhaling computer duster.

We reached out to reps for Nick, he had no comment.