The duke won't be stepping out of the public spotlight completely, though.
The duke, 96, who is stepping back from his royal duties after nearly 70 years, was described by a senior officer as a wonderful figurehead for all Marines to look up to.
The 1664 challenge raises money for The Royal Marines Charity. The name of the challenge refers to the year in which the corps was founded.
Theresa May led tributes to the royal following the announcement earlier this summer, saying he had given the monarch "steadfast support" during his years of service, the Press Association reported.
In his capacity of Captain General of the Royal Marines, the Queen's husband attended the finale of the 1664 Global Challenge - a 1,664-mile trek in aid of charity. He was appointed Captain General back in 2 June 1953, succeeding the late King George VI.
But from the demeanour of the Queen's Consort you would never have guessed he was retiring after carrying out 22,219 solo engagements since 1952.
Katie Ledecky wins 5th gold medal at World Championships
Two of his golds came in events that feature men and women on the same team, races Phelps never competed in at worlds. Sjostrom's time in the semi-finals broke the previous mark of 23.73 seconds set by Germany's Britta Steffen in 2009.
"The Queen wouldn't have been able to do it without him and I wonder how long the Queen will want to go on with royal duties without him". In 2016 alone, the Duke attended 200 events as he continued to represent the royal family with his own distinctive flair.
THE TELEGRAPH today wrongly declared that Prince Philip has died, publishing his obituary online.
Prince Philip has spent 52 days this year carrying out public engagements - more than the Queen and the Duke and Duchess of Cambridge.
The newspaper revealed the Duke's body is first expected to be taken to the Chapel Royal at St James's Palace in London, where it will likely lie until the day of the funeral.
It said he "may still attend events alongside the queen from time to time".
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