Backstreet Boys singer Nick Carter said he filed a restraining order against his brother Aaron Carter, claiming his younger sibling allegedly admitted to harboring thoughts of killing his pregnant wife.

Nick Carter, 39, said in a statement posted to his Twitter account Tuesday that he and sister Angel Carter went forward on the order of protection after their younger sibling displayed “alarming behavior.”

“In light of Aaron’s increasingly alarming behavior and his recent confession that he harbors thoughts and intentions of killing my pregnant wife and unborn child, we were left with no choice but to take every measure possible to protect ourselves and our family,” Nick Carter said.

The Backstreet Boys star is expecting his second child with wife Lauren Kitt Carter, who is due to give birth in less than a month.

Aaron Carter, 31, confirmed that he was served paperwork for a restraining order in a series of tweets Tuesday and denied the allegations laid out by his brother. The “Aaron’s Party” singer claimed that he hadn’t seen his brother in four years.

“I am astounded at the accusations being made against me and I do not wish harm to anyone, especially my family,” Aaron Carter said.

He also said that he and his brother Nick Carter were “done for life.”

Aaron Carter in a tweet appeared to imply his brother was attempting to have him institutionalized, referencing a California statute, Section 5150 of the Welfare and Institutions Code, where a person can be held without their consent for 72 hours if they prove to be a danger to themselves or others.

The former child star has opened up in recent years about his mental health issues and struggles. Aaron Carter said on a segment of the television show “The Doctors” last week that he suffered from multiple personality disorder, schizophrenia, acute anxiety, and manic depression. He said that he tried multiple times to get off a number of medications prescribed to him, such as Xanax and the antidepressant Trazadone.

“Look guys, I don’t want to be on these medications,” he said. “I tried to take myself off four times, off of all of them. And I sank into the darkest depression.”

Aaron Carter added that he was in the process of tapering off of Xanax and then “it’s done.”

Neither Aaron nor Nick Carter immediately responded to a request for comment from NBC News.