It’s been one month since Prince Philip, who was married to Queen Elizabeth for 73 years, passed away at Windsor Castle at the age of 99. Now, his true cause of death has finally been revealed as his death certificate has been released to the public.

Daily Mail reported that Philip’s cause of death is listed on his death certificate simply as being “old age.” The death certificate was certified by Sir Huw Thomas, head of the royal medical household.

“Old age” is accepted as the cause of death on a death certificate if the patient is over the age of 80, and if the doctor has cared for the patient personally over a lengthy period of time in which they watched him or her gradually decline. This being put down as Philip’s cause of death indicates that there was no other identifiable disease or injury that contributed to the death of the royal, including the heart condition that he had to undergo surgery for weeks before his passing.

Philip died “peacefully on April 9, according to Buckingham Palace, and his death was registered for days later with the Royal Borough of Windsor and Maidenhead by his private secretary, Brigadier Archie Miller-Bakewell. The certificate includes a nod to Philip’s Greek heritage as well as his own surname, Mountbatten, which he is reported to have fought for the royal family to use.

The document lists Philip’s full name as “His Royal Highness The Prince Philip, Duke of Edinburgh formerly known as Prince Philippos of Greece and Denmark formerly known as Philip Mountbatten.” His occasion is listed as “Naval Officer,” which is something he was very proud of, and “Prince of the United Kingdom.” The other occupation included on the death certificate is “husband of Her Majesty Queen Elizabeth II, The Sovereign.”

The Queen celebrated her 95th birthday less than two weeks after Philip’s death, and she marked the occasion by issuing a rare personal statement in which she thanked the public for the support they’ve given her since the passing of the man she was madly in love with for 73 years.

“I have, on the occasion of my 95th birthday today, received many messages of good wishes, which I very much appreciate,” the Queen said. “While as a family we are in a period of great sadness, it has been a comfort to us all to see and to hear the tributes paid to my husband, from those within the United Kingdom, the Commonwealth and around the world.”

“My family and I would like to thank you all for the support and kindness shown to us in recent days,” she added. “We have been deeply touched, and continue to be reminded that Philip had such an extraordinary impact on countless people throughout his life.”