Sondra died on November 3 although her death has only just been reported.
Her passing was promptly reported to authorities, but was not publicised until a RadarOnline story on Thursday.
It’s not clear why her death took so long to come to light.
Sondra was best known for the six films she made with Clint Eastwood in the late 1970s and early 1980s, including The Outlaw Josey Wales, Every Which Way But Loose, and Sudden Impact.
She and Clint also had a 13-year romantic relationship.
But she sued Clint for palimony in 1989 and for fraud in 1995 and brought separate action against Warner Brothers for allegedly conspiring with the actor to sabotage her directorial career.
She settled the three cases out of court.
Sondra was nominated for an Academy Award for Best Supporting Actress for 1968’s The Heart is a Lonely Hunter, her first film.
Sondra was born in 1944 as Sandra Louise Smith and raised in Shelbyville, Tennesse, US.
She changed her name to Sondra in her early 20s after winning a US talent search in 1967 for the part of teenager Mick Kelly in The Heart Is a Lonely Hunter.
Sondra starred opposite Alan Arkin, who was nominated for a Best Actor Oscar.
She also received Golden Globe nominations for Best Supporting Actress and Most Promising Newcomer.
More to follow…