Paul Reubens' primary cause of death was "acute myelogenous leukemia".
The actor - who was best known for playing Pee-wee Herman - passed away in July, aged 70, and it's now been revealed that he was fighting two forms of cancer before his death.
A copy of his death certificate - which has been obtained by The Blast - shows that the actor was battling blood cancer and metastatic lung cancer before he passed away.
Reubens ultimately lost his life because of "acute hypoxic respiratory failure". The condition occurs when the respiratory system "cannot adequately provide oxygen to the body, leading to hypoxemia".
The actor's death was announced by one his representatives.
The rep said in a statement: "Last night we said farewell to Paul Reubens, an iconic American actor, comedian, writer and producer whose beloved character Pee-wee Herman delighted generations of children and adults with his positivity, whimsy and belief in the importance of kindness.
"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."
What's more, the news was shared on Reubens' official Instagram page.
The announcement also included a personal statement from the actor, explaining why he decided to remain quiet about his cancer battle.
He wrote: "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."