“He was my father," Grammer tweeted. "I loved him."
Grammer, 62, shared a black and white photo of the two hugging.
Mahoney, who played Grammer’s father on the popular sitcom Frasier, died on Feb. 4 in Chicago.
The cause of death was not immediately revealed, but there are reports it was related to cancer complications.
“Watch Moonstruck, Say Anything and/or Frasier or anything you can with him in it and raise a glass to John. Remember him well,” tweeted Frasier co-star Peri Gilpin.
“Great actor — lovely kind human — any time you saw him you left feeling better - RIP John,” tweeted John Cusack, who starred with Mahoney in the 1980s movie classic Say Anything.
An official family statement detailing the exact cause of death is expected within the next several days.
We pay for juicy info! Do you have a story for RadarOnline.com? Email us at email@example.com, or call us at (866) ON-RADAR (667-2327) any time, day or night.