The Marvel Comics creator died from cardiac arrest, respiratory and congestive heart failure, according to his official death certificate from the Los Angeles Department of Health.
The certificate also reveals that Lee suffered from aspiration pneumonia, a complication in which a person inhales food, stomach acid or saliva into their lungs.
ET previously reported that Lee died on Nov. 12 at the Cedars-Sinai Medical Center in Los Angeles after he was rushed to the hospital following years of health issues. He was 95.
"Paramedics responded to Stan Lee's house in the Hollywood Hills early Monday morning for a medical emergency. He was transported to Cedar-Sinai Medical Center where he passed away shortly after," family attorney Kirk E. Schenck said in a statement at the time. "JC Lee and all of Stan Lee's friends and colleagues want to thank all of his fans and well-wishers for their kind words and condolences. Stan was an icon in his field. His fans loved him and his desire to interact with them. He loved his fans and treated them with the same respect and love they gave him."
Earlier this month, Lee's company, POW! Entertainment, also shared in a statement via Twitter that the comic mogul's family held a small funeral for him.
"Stan was always adamant that he did not want a large public funeral, and as such his family has conducted a private closed ceremony in accordance with his final wishes," the statement read. "Our thoughts and prayers continue to be with him."
Lee was a writer and editor and, at various points, both the publisher and vice president of Marvel Comics. He is the mastermind behind comic book creations like the Avengers, Fantastic Four, Spider-Man and X-Men. Hear more on Lee's legendary work in the video below.