“His pals from #MASH miss Bill powerfully. His kind strength, his grace and gentle humor weren’t acted. They were Bill. #WilliamChristopher,” Alda, 80, tweeted.
Christopher died at 5:10 a.m. PT on Saturday morning with his wife, Barbara, at his side. He was 84. A rep for the star told PEOPLE that he died “peacefully” and was “not in pain.”
Christopher’s son, John, told ABC that the actor died from a non-small cell lung carcinoma at his home in Pasadena, California.
John said Christopher was diagnosed with cancer a year and a half ago and had begun a new treatment last month before his health deteriorated. He entered hospice care on Monday, Dec. 26.
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Christopher played Father John Mulcahy on M*A*S*H alongside Alda who played Capt. Hawkeye Pierce.
Alda penned a touching tribute for another one of his M*A*S*H costars earlier this year. He remembered Wayne Rogers (who played Trapper John) in a piece for the The Hollywood Reporter following Rogers’ December 2015 death as a result of pneumonia.