Christina Sandera, Clint Eastwood's partner of around a decade, died in July from cardiac arrhythmia and coronary artery disease, USA TODAY can confirm.

According to a death certificate reviewed by USA TODAY on Monday, Sandera, a philanthropist, died in a Monterey County, California, hospital on July 18, two days after her 61st birthday. Her primary cause of death was cardiac arrhythmia, or a heartbeat with abnormal rate or rhythm, and atherosclerotic coronary artery disease was listed as another leading cause.

The New York Post was first to report Sandera's cause of death last month.

According to the U.S. National Heart, Lung and Blood Institute, people can develop atherosclerosis when plaque builds up in the arteries, causing them to narrow. Plaque is formed by "cholesterol, fat, blood cells and other substances in your blood."

Per the NHLBI, which is part of the National Institutes of Health, "Disease linked to atherosclerosis is the leading cause of death in the United States."

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Per Mayo Clinic, coronary artery disease can sometimes lead to sudden cardiac arrest, or the loss of heart activity due to the irregular rhythm of the heart.

Eastwood, 94, announced Sandera's death in a statement shared with outlets including The Hollywood Reporter and TheWrap on July 18.

“Christina was a lovely, caring woman, and I will miss her very much,” he reportedly said.

Christina Sandera remembered as 'a dedicated philanthropist and animal activist'

Two days later, the Monterey Bay National Marine Sanctuary Foundation paid tribute to Sandera, who was one of the nonprofit's board members, on social media.

The foundation described Sandera as "a dedicated philanthropist and animal activist" who was passionate about equestrian issues and marine life. She and Eastwood previously hosted a gala for the foundation at the Tehàma Clubhouse, which the "Million Dollar Baby" actor/director owns.

"Despite being connected to high-profile celebrity life, Christina often eschewed the spotlight. She was far more comfortable in her jeans, pigtails, and baseball hat, shoveling and tending to her beloved horses and animals. She was a 'roll up your sleeves' kind of person, always hands-on and deeply involved in her passions," the caption says.

Sandera and Eastwood kept their relationship relatively private over the past decade, aside from occasional appearances at high-profile events such as the premieres for 2018's "The Mule" and "The 15:17 to Paris."

The duo made their red carpet debut at the 2015 Academy Awards, where the Eastwood-directed "American Sniper" received six nominations.

In June 2014, Us Weekly reported that Eastwood was romantically involved with Sandera, who'd reportedly been an employee at the Eastwood-owned Mission Ranch hotel and restaurant in Carmel, California. Six months later, Eastwood finalized his divorce from his second wife, ex-TV reporter Dina Eastwood, after a 17-year marriage.

Eastwood was married to first wife Maggie Johnson from 1953 to 1984.