King County sheriff's spokesperson Sgt. Cindi West said the stabbing occurred at the woman's home in the 1300 block of SW 100th at approximately 5:50 p.m.
The accused son called 911 himself, and medics arrived to find the 69-year-old woman had been stabbed multiple times in the neck. Medics performed CPR on the woman, but she could not be revived. The woman has not been identified.
The 42-year-old son has been arrested.
"He's cooperative, I can tell you that," said West. "He said multiple times that he was sorry, and he was begging for us to save her."