AC/DC producer and The Easybeats' star George Young has died at the age of 70.
AC/DC said in a statement the band would not exist without Young's "help and guidance".
"As a musician, songwriter, producer, advisor and much, much more, you could not ask for a more dedicated and professional man," the statement read.
"You could not ask for a finer brother. We will always remember him with gratitude and hold him close to our hearts."
George was the eldest brother of Australian rock legends Malcolm and Angus Young. He was born in Scotland in 1946 but emigrated to Australia with his family when he was still a child.
He shot to fame in the '60s as a guitarist for the Sydney-based rock band The Easybeats. While the band broke up in 1970, he and lead guitarist Harry Vanda were later inducted into the ARIA Hall of Fame.
Young was also known for co-producing AC/DC's early albums, including TNT, Dirty Deeds Done Cheap, Powerage, High Voltage and Let There Be Rock.
Prior to AC/DC's formation, Young was the vocalist for the rock group Marcus Hook Roll Band, with his brothers on guitar.
There was an outpouring of grief on social media on Monday afternoon after Young's death was announced. Rock legend Jimmy Barnes wrote on Twitter that the songwriter's death was a "huge loss for music".
"A great songwriter, producer and a great human being," he said.
AC/DC posted the following on their Twitter at about 5.30pm this evening -
"It is with pain in our heart that we have to announce the passing of our beloved brother and mentor George Young. Without his help and guidance there would not have been an AC/DC.
As a musician, songwriter, producer, advisor and much, much more, you could not ask for a more dedicated and professional man.
As a brother, you could not ask for a finer brother. For all he did and gave to us throughout his life, we will always remember him with gratitude and hold him close to our hearts".
SOURCE: Sydney Morning Herald.