Los Angeles, California - Paul Reubens was battling two forms of cancer when he passed away in July, according to a new report on the Pee-wee Herman actor's tragic death.

The actor and comedian's death certificate lists "acute hypoxic respiratory failure" as the immediate cause of death, according to a Friday report by People. Acute hypoxic respiratory failure occurs when the respiratory system cannot provide enough oxygen to the body.

The underlying primary cause of death was recorded as acute myelogenous leukemia, a type of blood and bone marrow cancer. Reubens had also reportedly been diagnosed with metastatic lung cancer.

In a July 31 social media post announcing his death, Reubens revealed that he had been privately battling cancer for years.

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"Please accept my apology for not going public with what I've been facing the last six years," read Reubens' posthumous statement. "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."

A statement accompanying Reubens' note 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."

Reubens was best known for portraying the beloved character Pee-wee Herman.