Catherine O’Hara died from a pulmonary embolism, with cancer as the underlying cause, according to a Los Angeles County death certificate issued Monday, The Associated Press reported.

The certificate lists the pulmonary embolism, which occurs when a blood clot blocks an artery in the lungs, as the immediate cause of the actor’s Jan. 30 death at age 71. Rectal cancer was the long-term cause.

The oncologist who signed off on the certificate indicated that he had been treating O’Hara since March of last year, and last saw her on Jan. 27. She died at a hospital in Santa Monica, California. She was cremated, according to the document.

The beloved Canadian-born comic actor and “SCTV” alum starred as Macaulay Culkin’s mother in two “Home Alone” movies and won an Emmy as the dramatically oblivious wealthy matriarch Moira Rose in “Schitt’s Creek.”

Her death came as a surprise to most fans, and an initial statement from her representatives said only that she died “following a brief illness.”

Over the course of her five-decade career, O’Hara had roles on numerous television series, including “Six Feet Under,” “Curb Your Enthusiasm” and “The Studio.”

She also appeared in several films, including the HBO production “Temple Grandin,” for which she received an Emmy nomination. 

In 2015, O’Hara teamed up with her longtime friend and fellow”SCTV” alum Eugene Levy for the sitcom “Schitt’s Creek.” The two also appeared in seven movies together throughout their careers, including four Christopher Guest mockumentaries.

Her collaborators and costars over the years, including Levy, Culkin, Guest and Pedro Pascal, paid her loving tribute after her death.

“Mama. I thought we had time,” Culkin posted on Instagram, along with side-by-side images of the two of them from “Home Alone” and the two together at Culkin’s Hollywood Walk of Fame ceremony. “I wanted more. I wanted to sit in a chair next to you. I heard you. But I had so much more to say. I love you. I’ll see you later.”

Michael Keaton, who starred alongside O’Hara in “Beetlejuice” and “The Paper,” wrote on Instagram, “She’s been my pretend wife, my pretend nemesis and my real life, true friend. This one hurts. Man am I gonna miss her.”

Seth Rogen, whom O’Hara had worked with recently on the Apple TV series “The Studio,” wrote on Instagram that she was “hysterical, kind, intuitive, generous… she made me want to make our show good enough to be worthy of her presence in it.”

“We’re all lucky we got to live in a world with her in it,” he added.