"He was my father. I loved him," Grammer tweeted.
The simple message captioned a photo of Mahoney with his arms wrapped affectionately around Grammer's neck in an embrace.
Mahoney died in hospice care Sunday in Chicago at the age of 77.
He was my father. I loved him. pic.twitter.com/3mGcyEMxoy— Kelsey Grammer (@KelseyGrammer) February 7, 2018