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Hugh Hefner died of cardiac arrest and respiratory failure.

The 91-year-old Playboy founder’s death certificate, which was obtained by Page Six via The Blast, also revealed he had been battling E. coli and septicemia (blood poisoning) for six days prior to his passing on Sept. 27.

The doc explains that Hef’s infection was “highly resistant to antibiotics.”

He passed away in his famed mansion in Los Angeles, which will undergo massive renovations under its new owner, Daren Metropoulos.

The iconic publisher was laid to rest in a private memorial Saturday.

On Monday, Hef’s wife Crystal made her first statement since his passing.

“I am heartbroken. I am still in disbelief,” she told People. “He gave me life. He gave me direction. He taught me kindness. I will feel eternally grateful to have been by his side, holding his hand, and telling him how much I love him. He changed my life, he saved my life. He made me feel loved every single day.”