Megadeth frontman Dave Mustaine has revealed a lifelong suspicion that he may not have been his mother's biological child, a possibility brought to the forefront by a recent conversation with his sister. The rocker details these revelations in his upcoming memoir, "In My Darkest Hour."

Mustaine, 64, grew up in a household dominated by his mother's devout Jehovah's Witness faith, a religious environment he describes as "religious abuse." This upbringing, he has stated, led to alienation from his peers and contributed to his teenage rebellion, during which he explored occult practices before co-founding Metallica and later forming Megadeth.

His memoir explores the "weird and dysfunctional household" he experienced, noting his father's departure when Mustaine was four and his mother's descent into religious fervor. Mustaine recounts dreams where his mother and father were absent, replaced by his eldest sister, Michelle, who he felt was unusually protective. He also noted a stronger resemblance to his sisters than to his mother, fueling his suspicion that one of his sisters might have had a child out of wedlock and had the child – him – raised by their mother.

This long-held suspicion was recently stirred by a conversation with his middle sister, Suzanne, who is in hospice care with Parkinson's and dementia. During a fragmented discussion, aided by her assistant, Suzanne seemed to confirm that "David" was her "baby." Mustaine considers the possibility that Suzanne was referring to him colloquially as a "little brother," but also ponders a "more sinister" interpretation.

If Suzanne were his biological mother, it would have been more scandalous given she was only 15 when he was born, a fact Mustaine suggests could explain her past bitterness towards him. However, definitive answers remain elusive. His mother and his sister Michelle are deceased. His youngest sister, Debbie, is too close in age to have memories of his birth, and Suzanne is not lucid enough to provide clarity.

Mustaine, who converted to Christianity around 2002, has spoken about overcoming drug and alcohol abuse and battling throat cancer in 2019. He credits his conversion and his "tight family"—his wife Pam and their children Electra and Justis—with providing strength. He views his current family life as a blessing, contrasting it with the fractured origins he escaped.

"In My Darkest Hour" is set to be published on September 8 by Da Capo, an imprint of Hachette Book Group.