Ambrosia Founding Member Christopher North Cause of Death Revealed

Christopher North -- a founding member and keyboardist for '70s and '80s rock band Ambrosia -- died after a bout with pneumonia, TMZ has learned.

His brother, Richard North, tells TMZ ... Christopher was hospitalized for about 3 weeks before he succumbed to complications related to pneumonia.

As we reported, Christopher previously battled throat cancer and was struck by an out-of-control vehicle in Santa Monica last October, which left him hospitalized for about 2 months. His brother tells us he had been admitted to the hospital twice since then.

We're told Christopher's cancer and car accident weakened his body ahead of his bout with pneumonia, and he ultimately took his last breath while in the care of doctors.

Richard referred TMZ to Ambrosia cofounder David Pack's most recent social media post for more information. David and Ambrosia's official Facebook page announced Christopher's death ... with David describing his longtime pal as a multi-talented musician with strong vocals and unwavering passion.

He also gushed about his stage presence, writing ... "And if you saw the original band live you couldn’t keep your eyes off of his wild and engaging stage persona. Most nights he’d bloody his hands on the B3 or break off keys. Ferocious is an understatement."

Christopher formed Ambrosia in 1970 with David, bassist Joe Puerta, and drummer Burleigh Drummond.

A source connected to the band says no memorial plans have been made at this time.

He was 75.