EXCLUSIVE

John Mahoney's death was caused by multiple health complications, which included brain disease and lung cancer.

Our sources say the "Frasier" star's official causes of death include brain disease, lung cancer and seizures. We're told Mahoney also suffered from kidney disease and diabetes.

We broke the story ... Mahoney died Sunday in Chicago while in hospice care.

Our sources say Mahoney was cremated.

Mahoney played Kelsey Grammer's cranky father, Martin Crane, for 11 seasons on the hit sitcom. Shortly after John's death, Grammer posted, "He was my father. I loved him."

He most recently had a recurring role starring on the TV show "Hot in Cleveland," which ended in 2014. He's also had appearances on movies like 'American President,' "Say Anything..." and "Eight Men Out" over the course of more than 30 years in the industry.

John was 77. RIP