Pop stars Nick and Aaron Carter are in mourning following the sudden death of their father.

Robert Carter died on Tuesday night (16May17), aged 65.

A cause of death has yet to be revealed, but according to TMZ.com, the news emerges shortly after singer Aaron shared a Twitter post about his dad, known as Bob, being found unconscious.

The tweet has since been deleted, and instead, the 29-year-old wrote on Wednesday (17May17), "My heart is Completly shattered I'm in shock and I loved my dad so much (sic). #RIP DADDY I Love You."

"This is the last pic I have (of) my dad," Aaron added as he shared a snap of the smiling father and son, who appeared together on the family's short-lived reality show House of Carters in 2006.

He also took to Instagram to further express his heartache: "My heart is broken," he captioned an old snap of the pair. "We are so hurt we lost you poppa way too soon (sic). You were never human to me, you were always my real life super hero #BobCarter #RIP #MyDaddy".

Meanwhile, his older brother Nick Carter, who had been estranged from his parents, has asked the press for privacy as his family comes to terms with the tragedy.

"I am heartbroken to share the news that our father, Robert, passed away last night...," the Backstreet Boys star posted. "While we learn more about the cause of death, and begin the grieving process, we ask that our privacy be respected at this difficult time."

A former bar owner in New York, Carter Sr. was married to Nick and Aaron's mother, Jane, until their divorce in 2003. They also had three daughters together: Bobbie Jean, Aaron's twin sister Angel, and Leslie, who died from a drug overdose in 2012, aged 25.

Nick, who has battled substance abuse in the past, has previously revealed his mom and dad partly blamed him for Leslie's death, prompting him to skip his sister's funeral. Jane and Bob were also not present for Nick's marriage to Lauren Kitt in 2014.

It is not known if the singer was still estranged from his dad at the time of his passing.