A 59-year-old man was shot to death by his stepfather when he threatened his mother with a knife in Encinitas, authorities said Friday.

The shooting occurred Tuesday at a home in the 1200 block of Greenlake Drive, San Diego County sheriff’s Lt. Michael Blevins said.

Robert Dean was taken to a hospital where he was pronounced dead, Blevins said.

Barbara Miller, 80, called the sheriff’s department to report her adult son was threatening her, Blevins said.

The stepfather, identified as 74-year-old William Miller, “armed himself with a gun and shot the son,” Blevins said.

Barbara Miller was not injured and William Miller was questioned by detectives, Blevins said.

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