Only one day ago it was announced that the co-founder of Australia's most successful rock groups, AC/DC, Malcolm Young, has officially retired after a career spanning over four decades as the rhythm guitarist.

Malcolm Young
Malcolm Young [L] with the rest of AC/DC

In April, the 61 year-old musician initially left AC/DC because he was struggling with an undisclosed illness, and the they asked that people respect the privacy of Malcolm and his family at this difficult time.

"Unfortunately, due to the nature of Malcolm's condition, he will not be returning to the band," the statement said. "AC/DC will undertake a world tour in support of 'Rock or Bust' in 2015. Stevie Young, nephew of founding members Angus and Malcolm Young, plays rhythm guitar on 'Rock or Bust' and will accompany the band on tour."

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It is now believed that Malcolm was forced to call time on his rock career because he is suffering from an ongoing battle with dementia and has moved into full-time care in a nursing home facility in his native Australia, reports the Sydney Morning Herald.

Sources told the newspaper that the home, Lulworth House in Elizabeth Bay, is located in Sydney's eastern suburbs and specialises treating individuals with the degenerative disease.

"If you were in the room with [Malcolm Young] and walked out then came back in one minute later he wouldn't remember who you are. He has a complete loss of short term memory. His wife Linda has put him in full-time care," the insider said.

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The band also confirmed they will head back onto the road in 2015 for a world tour and to promote their forthcoming 15th studio album 'Rock or Bust.' As Malcolm wrote the majority of the lyrics, his younger brother and lead guitarist, Angus Young, will be taking on the scribing responsibilities.

AC/DC have sold more than 200 million albums worldwide.