AC/DC founding member Malcolm Young is suffering from dementia, his family said Tuesday.
His family confirmed the diagnosis in a statement to People and thanked fans for respecting their privacy.
Malcolm Young, 63, formed the rock band in the early '70s with younger brother Angus Young, now 59. The elder Young's retirement was announced last Wednesday along with the release date of AC/DC's next album, Pop & Hiss reported.
At that time, the illness was unspecified, with the band's statement referring only to "Malcolm's condition." Stevie Young will be taking over his uncle's spot on rhythm guitar.
The band announced the guitarist was taking a break for health reasons back in April, but didn't indicate it was a permanent situation until last week.
Lead singer Brian Johnson told Classic Rock magazine in June that Malcolm Young was hospitalized.
"He's such a strong man," Johnson said at the time. "He's a small guy but he's very strong. He's proud and he's very private, so we can't say too much. But fingers crossed he'll be back."