The death of Margot Kidder, who famously played Lois Lane in the "Superman" movies of the 1970s and '80s, has been ruled a suicide.

In a statement provided to The Associated Press on Wednesday, Park County Coroner Richard Wood said Kidder’s death earlier this year was "a result of a self-inflicted drug and alcohol overdose." No further details were released.

"It's a big relief that the truth is out there," Kidder's daughter Maggie McGuane told the outlet. "It's important to be open and honest so there's not a cloud of shame in dealing with this."

Kidder died on May 13 at her home in Livingston, Montana. She was 69.

The late actress, who started her career in 1968 and got her big break in the 1973 film "Sisters," starred opposite Christopher Reeve in "Superman" and three sequels. She continued to act in many movies and TV shows, most recently the 2017 film "The Neighborhood."

Kidder also battled bipolar disorder and was homeless for a short time in 1996. That same year, Kidder was working on her autobiography when her computer was infected by a virus causing her to lose all of her files. She became paranoid and disappeared for four days until she was found in a stranger's backyard and taken to Olive View Medical Center by police.

Five months after her manic incident, she opened up to People magazine saying she had "mood swings that could knock over a building."

Kidder said at the time she was first diagnosed with bipolar disorder eight years earlier, but refused to take the lithium that was prescribed to her.

"It’s very hard to convince a manic person that there is anything wrong with them," Kidder said. In 2007, she revealed she had not suffered a manic episode in 11 years and credited orthomolecular medicine.

In what may have been her final interview before her death, Kidder told WWJ's Sandra McNeill on May 9 she was "sad but not that sad" when her "Superman" co-star Christopher Reeve became a quadriplegic.

"The truth is he was kind of an a-----e," Kidder said before adding they had a brother-sister relationship and bickered a lot.

Kidder was married to novelist Thomas McGuane with whom she had a daughter, Maggie. She went on to marry actor John Heard in 1979 only to divorce six days later. Her third marriage was to French film director Philippe de Broca which lasted from 1983 to 1984.

Fox News' Sasha Savitsky and The Associated Press contributed to this report.