The 43-year-old Backstreet Boys member called Spears' conservatorship "grotesque" and claimed that the last time he saw her "she just didn’t know who was there."
The former boy banders apparently did not like one another, but have since developed a "mutual respect."
The boy band sang "I Want It That Way" from their respective homes as part of a coronavirus benefit concert.
Alicia Keys, Billie Eilish, Mariah Carey, the Backstreet Boys, Tim McGraw and Billie Joe Armstrong are scheduled to take part in the event airing Sunday on Fox TV.
"You should've taken it as a compliment dick," Carter wrote when an artist from Berlin said the singer used a picture of his work without attribution or permission.
They wanted it that way.
The "Mary Poppins Returns" star took to the mic for "I Want It That Way."
Melissa Schuman, a former member of the pop group Dream, claimed the singer raped her in 2003.
Melissa Schuman, a former member of the pop girl group Dream, accused the Backstreet Boy of raping her in 2002.
The Los Angeles County district attorney is reviewing allegations made by Melissa Schuman against Carter.