Getty

Stunning new details surrounding Jim Irsay 's death in May ... the legendary Indianapolis Colts owner reportedly passed away at the Beverly Hills Hotel while under the care of an addiction specialist.

The Washington Post obtained the death certificate for 65-year-old Irsay ... which listed his cause of death as cardiac arrest due to acute pneumonia, chronic atrial fibrillation and cardiac arrhythmia on May 21. Getty

The document is signed by Dr. Harry Haroutunian , who'd been tending to Irsay at the hotel in the days before his death, and he told police the cause of death was natural.

According to WaPo, officials elected not to investigate or conduct an autopsy ... as his death was not considered sudden, violent or unexpected. Beverly Hills PD investigated the incident

See Full Page