She made her film debut in 1968 in The Heart Is a Lonely Hunter, for which she was nominated for an Academy Award for Best Supporting Actress.
Locke died on 3 November and, while authorities were promptly notified at the time of death, it is not yet understood why the news has taken so long to be reported. A subsequent death certificate has confirmed that the 74-year-old died in Los Angeles after suffering a cardiac arrest.
The heart attack was brought on by an ongoing battle against breast and bone cancer.
Locke, who dated Clint Eastwood for almost 13 years, was best known for the six films alongside her partner which included the likes of The Outlaw Josey Wales,Dirty Harry and Sudden Impact.