The music world is mourning yet another loss of a heavyweight. Glenn Frey, founding member, guitarist, and songwriter for The Eagles passed away on Monday at the age of 67.

According to the official word, Frey died from complications of multiple illnesses.

“It is with the heaviest of hearts that we announce the passing of our comrade, Eagles founder, Glenn Frey, in New York City on Monday, January 18th, 2016. Glenn fought a courageous battle for the past several weeks but, sadly, succumbed to complications from Rheumatoid Arthritis, Acute Ulcerative Colitis and Pneumonia. The Frey family would like to thank everyone who joined Glenn to fight this fight and hoped and prayed for his recovery. Words can neither describe our sorrow, nor our love and respect for all that he has given to us, his family, the music community & millions of fans worldwide,” read a statment posted to The Eagles’ Facebook page.

Now, Frey’s good friend and collaborator Bob Seger has revealed some more details surrounding Frey’s illness and death.

According to Seger, Frey had been in the hospital since November.

“First he caught one set of pneumonia, then he caught a very virulent set of pneumonia,” Seger told the Detroit Free Press. “They were trying like hell to keep him alive. He’d been at Columbia University Medical Center since November. (Eagles manager) Irving (Azoff) pulled every ace out of the hole — he had the eight best specialists working on Glenn. About a month ago, they had to throw up their hands.”

Seger, who met Frey in the 1960s, said Frey was a joy to be around.

“I knew him for 50 years,” Seger told Billboard. “He was a great kid. I always kind of thought of him as my baby brother, a little bit. He was f—ing brilliant. He was a joy to be around. I always looked forward to seeing him. It was always memorable. He had an amazing sense of humor and was just smart, whip-smart.”

RIP Glenn Frey.