The stage, TV and film actress, married to actor Kirk Douglas from 1943 to 1951, died this month at age 92 after battling cancer.
At a Monday screening of "Ant-Man," in which the two-time Oscar winner plays reclusive-billionaire scientist Dr. Hank Pym, Michael Douglas told the Associated Press that his mother "had an incredible sense of dignity and was a class act."
The "Wall Street" star, 70, referred to Diana as "a lady" who had a strong influence on him, despite him letting her down "a couple of times," though he did not elaborate on the details.
Diana costarred with Michael in the 1970s TV series "The Streets of San Francisco" and reunited with him and Kirk in the 2003 film "It Runs in the Family." She remarried twice and eventually rekindled her friendship with ex-husband Kirk, who will turn 99 in December.
In March, the "Fatal Attraction" actor, a U.N. messenger of peace, penned an op-ed for the Los Angeles Times in which he talked about a brush with anti-Semitism in Europe and his own history with it because his mother was not Jewish.
Judaism has become a major talking point for the outspoken actor: He recently faced criticism from the Orthodox Jewish community after being awarded the Genesis Prize, a $1-million honor set up by Russian billionaires to celebrate Jewish culture, because he is the product of an interfaith marriage and married to a non-Jew, actress Catherine Zeta-Jones.