Director Rob Reiner and his wife, Michele, were the two people found dead at a Los Angeles home, police have told the Associated Press.
Investigators believe they suffered stab wounds, and a family member is being questioned by investigators, the official said.
The Los Angeles Fire Department said it responded to a medical aid request on Sunday afternoon and found a 78-year-old man and a 68-year-old woman dead inside.
Detectives with the Robbery Homicide Division were investigating an "apparent homicide" at Reiner's home, Captain Mike Bland with the Los Angeles Police Department told the Associated Press.
There is reportedly a heavy police presence at the home, according to US publication Variety.
Rob Reiner directed classic films such as Stand By Me, Misery, When Harry Met Sally, and The Princess Bride.
He also acted in Sleepless in Seattle, The First Wives Club, The Wolf of Wall Street, and, most recently, appeared in the TV show The Bear.
Reiner married photographer Michele Singer in 1989, and they owned the home in Brentwood together.
He was also a major fundraiser for the US Democratic Party and was critical of President Donald Trump.
Los Angeles Mayor Karen Bass called Reiner's death a devastating loss for the city.
"Rob Reiner's contributions reverberate throughout American culture and society, and he has improved countless lives through his creative work and advocacy fighting for social and economic justice," Bass said in a statement.
"An acclaimed actor, director, producer, writer, and engaged political activist, he always used his gifts in service of others."
Rob Reiner was the son of comedy legend Carl Reiner.
The two met while he was directing "When Harry Met Sally" and have three children together.
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