AC/DC's Angus Young says his brother Malcolm's dementia was evident six years ago

This file photo taken on March 22, 2000 shows Australian guitarists and brothers Angus (left) and Malcom Young (right) of the hard rock group AC/DC inaugurating a street named after them in Leganes, near Madrid in Spain. Angus Young said he first not
This file photo taken on March 22, 2000 shows Australian guitarists and brothers Angus (left) and Malcom Young (right) of the hard rock group AC/DC inaugurating a street named after them in Leganes, near Madrid in Spain. Angus Young said he first noticed something amiss with brother Malcolm six years ago, and his dementia worsened until he could no longer remember his own songs. -- PHOTO: AFP

Sydney (Agence France-Presse) - AC/DC guitarist Angus Young says he first noticed something amiss with brother Malcolm six years ago, and his dementia worsened until he could no longer remember his own songs.

Malcolm Young, 61, who co-founded the veteran Australian band that went on to become one of the biggest grossing groups of all time, retired this year and is now believed to be in a Sydney care facility.

Angus Young said he first noticed something was wrong when they were recording their last album, Black Ice, in 2008, a record that shot to the top of the charts in 31 countries.

"When we were writing songs together, me and him, then, it was noticeable," he told ABC television in an interview on Monday.

"It was just strange things, you know? I mean, memory things. Malcolm was always very organised (so) it was kind of strange," he added.

"For the first time I'd seen him disorganised, being confused about a lot of things. That's when it kind of, you know, hit me. Something was not right with him."

Angus said he spoke to Malcolm, telling him he did not need to keep going if he did not feel up to it. "And he said, 'No I'll keep going, you know, until I can't'," he said, adding that eventually his brother could no longer remember his own songs.

Despite the setback, the high-voltage group decided to stay together, which was Malcolm's wish, and they have a new album, Rock Or Bust, out this week and a world tour scheduled for 2015.

"He said, 'Keep making music'," lead singer Brian Johnson said of Malcolm Young when he knew he could no longer continue.

"Without any of that sympathy stuff, you know, there was none of that stuff around.

"And he just said to keep doing it. That's the way he talked - straight shooter. So we did, and it was great."

The band hired Young's cousin Stevie as his replacement.

Since then they have had to deal with another crisis after drummer Phil Rudd was arrested in New Zealand and charged with threatening to kill and possession of cannabis and methamphetamine.

Under New Zealand law, threatening to kill can attract a seven-year sentence and it remains unclear whether he can continue with the band. The Young brothers founded AC/DC in Sydney in 1973, and they have gone on to sell more than 200 million albums.