The queen's physician, who has been caring for both Her Majesty and Prince Philip since 2014, according to People, has revealed the duke's cause of death.
Per his death certificate, reportedly obtained by The Telegraph, the 99-year-old Duke of Edinburgh died of "old age" – an acceptable cause of death by Sir Huw Thomas, the head of the royal medical household, if the patient is over 80 years old and the physician has personally cared for them over a long period.
Prince Philip died on 9 April after a month-long stay in hospital, though he'd been battling with health issues for years; he officially retired from royal duties in 2017.
A funeral service was held on 17 April and attended by a select few members of the royal family.
Following the service and on her 95th birthday, the queen released a statement thanking the public for their support. "We have been deeply touched, and continue to be reminded that Philip had such an extraordinary impact on countless people throughout his life," she said.