Clint Eastwood's longtime partner, Christina Sandera, died on Thursday, July 18. She was 61.

Sandera's cause of death was due to cardiac arrhythmia, the Monterey County Dept. of Health stated on a death certificate obtained by Fox News Digital.

"Atherosclerotic coronary artery disease" was listed as an underlying cause which contributed to her death. 

CLINT EASTWOOD'S DAUGHTER REMEMBERS STAR'S LONGTIME GIRLFRIEND AFTER HER DEATH AT 61: ‘A DEVASTATING LOSS’

A heart arrhythmia is an irregular heartbeat, according to the Mayo Clinic. 

Coroners performed an autopsy on Sandera before her body was cremated, according to the report.

Sandera, a philanthropist, died at 1:46 p.m. Her manner of death was listed as "natural" on the official report.

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Eastwood and Christina were relatively low-profile about their relationship, having met nearly a decade ago while she was employed at his Mission Ranch Hotel and Restaurant in Carmel-by-the-Sea near Monterey, California.

"Christina was a lovely, caring woman, and I will miss her very much," Eastwood told The Hollywood Reporter shortly after her death.

Clint's daughter, Morgan Eastwood, mourned the loss of Sandera in an Instagram post shared Sunday.

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"A devastating loss for our whole family," Morgan wrote. "Thank you Christina for being a good partner to my Dad. You will be missed."

Prior to his relationship with Sandera, Eastwood was married twice. His first marriage was to model Maggie Johnson from 1953-64. The former couple didn't finalize their divorce until 1984.

Eastwood then married Dina Ruiz in 1966 and the couple divorced in 2014.

The award-winning actor is a father of eight: Laurie Murray, Kimber Eastwood, Kyle Eastwood, Alison Eastwood, Scott Eastwood, Kathryn Eastwood, Francesca Eastwood and Morgan Eastwood.