Reubens' immediate cause of death was recorded as acute hypoxic respiratory failure, a condition that occurs when the lungs cannot release enough oxygen into the blood, according to a death certificate obtained by PEOPLE.
The death certificate also said Reubens battled two types of cancer at the time of his death: acute myelogenous leukemia (cancer of the blood and bone marrow), which was listed as a sequential underlying cause, and metastatic lung cancer. He kept his diagnoses private until after his death.
Jamie McCarthy/Getty Paul Reubens
Reubens, an actor and comedian who was best known for his beloved man-child character Pee-wee Herman but also appeared in numerous other film and TV projects, died July 30.
In a posthumous statement posted to his social media accounts, he said, "Please accept my apology for not going public with what I've been facing the last six years. I have always felt a huge amount of love and respect from my friends, fans, and supporters. I have loved you all so much and enjoyed making art for you."
An accompany statement said, "Paul bravely and privately fought cancer for years with his trademark tenacity and wit. A gifted and prolific talent, he will forever live in the comedy pantheon and in our hearts as a treasured friend and man of remarkable character and generosity of spirit."