Prince William and Prince Harry’s 20-Year-Old Cousin's Cause of Death Revealed

Prince William and Prince Harry's 20-year-old cousin Rosie Roche died from a traumatic head injury.

Roche was found dead in her home in England last week and her cause of death was reported Tuesday by multiple British news outlets, citing the Wiltshire and Swindon coroner.

William and Harry's cousin was the grandchild of Princess Diana's uncle ... and her dead body was reportedly discovered by her mother and sister, and a gun was found nearby.

Coroner Grant Davies previously told The Sun police deemed Roche's death as "non-suspicious" with "no third-party involvement" ... which makes it sound like cops believe she may have taken her own life.

Roche was a student at Durham University, where she was reportedly pursuing a degree in English Literature.

The Yorkshire Post published an obituary Friday, saying Roche was an "incredible sister" to her two siblings. The obit also said she will be laid to rest in a private funeral and memorial service.