"We did everything we could to try to pull him out of the mental state that he was in, but that level of anguish was untouchable."
Meanwhile, a cardigan owned by Kurt recently sold at auction for $334,000 (NZ $521,000).
The Nirvana frontman wore the garment during the band's MTV 'Unplugged' performance in 1993, and the stained cardigan has not been cleaned since.
The item went under the hammer in New York on Saturday, and is said to be the most expensive sweater ever sold at auction.
According to Darren Julien, the president of Julien's Auction, the cigarette-burned cardigan is "the holy grail of any article of clothing that he ever wore".
The music icon's custom-made Fender Mustang guitar was also sold at the auction for $340,000, having spent several years on display at the Rock and Roll Hall of Fame.