Betty White’s cause of death has been revealed.

The Golden Girls star, who passed away at age 99, died due to a cerebrovascular accident, according to her death certificate obtained by PEOPLE on Monday. TMZ was the first to report the news.

A cerebrovascular accident, commonly known as a stroke, is a loss of blood flow to part of the brain, which damages brain tissue. It is typically caused by blood clots and broken blood vessels in the brain.

According to the death certificate, White suffered a stroke six days before her death.

A source tells PEOPLE “It was a mild stroke. She died peacefully in her sleep.”

White’s longtime agent and friend Jeff Witjas also tells PEOPLE: “Betty passed in her sleep peacefully without pain. To me this is the most important thing and brings me comfort as her dear friend. Anything else is private to Betty.”

White’s agent and close friend Jeff Witjas first confirmed to PEOPLE in a statement that the beloved actress “died peacefully in her sleep at her home” that morning.

“Even though Betty was about to be 100, I thought she would live forever,” Witjas said. “I will miss her terribly and so will the animal world that she loved so much. I don’t think Betty ever feared passing because she always wanted to be with her most beloved husband Allen Ludden. She believed she would be with him again.”

Days later, Witjas spoke out again and denied false social media claims that the actress died due to effects related to a COVID-19 booster shot administered on Dec. 28.