Anne died at her Beverly Hills home on Thursday, April 30. Her cause of death was not disclosed.
Her passing comes one year after Kirk died in February 2020 after 66 years of marriage. The couple shared sons Peter and Eric together.
"Anne was more than a stepmother, and never 'wicked.' She brought out the best in all of us, especially our father. Dad would never have had the career he did without Anne's support and partnership," Michael said in a statement obtained by PEOPLE. "Catherine [Zeta-Jones] and I and the children adored her; she will always be in our hearts."
Michael continued, "My father could never keep a secret. Anne was just the opposite, That's why I was so moved when I read their co-authored book, Kirk and Anne, in which she talked about her early life in Germany; her war years in occupied Paris; and her career before she met my father. She also included their private correspondence, which gave me new insights into their courtship and marriage."
Anne and Kirk met in 1953 while he was filming Act of Love in Paris and she was a film publicist at the time. The pair tied the knot a year later in Las Vegas.
The couple set up The Douglas Foundation together, which went on to donate millions to a variety of organizations ranging from the Children’s Hospital Los Angeles to the Motion Picture & Television Fund. She also founded the The Anne Douglas Center for Women at the Los Angeles Mission.
"We are deeply saddened to learn of the death of Mrs. Anne Douglas, beloved widow of Kirk Douglas. Together the Douglas family has been deeply involved in the Los Angeles Mission's efforts to restore the lives of our city's homeless," the Mission's president, CEO Troy Vaughn, said in a statement.
He continued, "More than thirty years ago, Anne Douglas' driving passion led the building of the Mission's women's center, the Anne Douglas Center for Women. As Anne herself put it: 'If I had but one wish, I think becoming a recognized patron of homeless men and women would be it. I hope together we will be able to alleviate their plight entirely.'
"The Los Angeles Mission and the Anne Douglas Center is proud to uphold her legacy and tireless commitment. Rest In Peace, Anne. We love you," Vaughn concluded.
Last week, Michael marked Anne's birthday with a family photo on Instagram. "Happy Birthday Anne Douglas! We love you! ❤️ Michael, Catherine, Carys, & Dylan," he captioned the picture.
Michael's mother, Diana Douglas, who was Kirk's first wife passed away in 2015.
"I often wonder what would have happened to me if I hadn't married Anne. I might not have survived without her business acumen and her finely honed instincts," Kirk once said.