The Duke of Edinburgh's cause of death has been officially recorded as "old age."

Prince Philip died on April 9, just weeks after he reunited with the Queen following a month-long stay in hospital. 

The death certificate reveals that his death was certified by Sir Huw Thomas, the head of the royal medical household, who was knighted earlier this year.

He declared the cause simply as "old age", an accepted description if the patient is over 80 and if the doctor has personally cared for them for a long period, observing a gradual decline.

It suggests there was no other identifiable disease or injury that contributed to the death, including the heart condition that forced him to undergo a surgical procedure just weeks before he died. 

Dad-of-four Philip was the longest-serving consort in British history, dedicating decades of his life to royal duty, serving the nation at the monarch's side.

The Royal Navy hero had a glittering career in the military, and was one of the last surviving UK veterans to have served in the Second World War, when he witnessed the historic surrender of Japanese forces in 1945.

His greatest legacy is likely to be the pioneering Duke of Edinburgh’s Award for youth, which he founded in 1956 and has since been expanded to almost 150 countries.

Active with many charities, he was a patron, president or member of more than 700 organisations during his lifetime.

The Duke had spent the last year isolating with his beloved wife at Windsor Castle along with a scaled back team of royal staff.