The Duke of Edinburgh will meet Royal Marines who have completed a mammoth 1,664 mile trek on Wednesday - his final official royal event before he retires from public engagements.
In the grounds of Buckingham Palace, Philip will celebrate the achievements of servicemen who have taken part in the 1664 Global Challenge, a series of strength and endurance feats raising funds and awareness for the Royal Marines Charity.
The Queen's Consort announced in May he would be retiring from royal engagements after more than 65 years supporting the monarch in her role as head of state and attending events for his own charities and organisations.
Philip, 96, was praised at the time for his public service with Prime Minister Theresa May leading the tributes saying he had given the Queen "steadfast support'', while Labour leader Jeremy Corbyn said the Duke's ''clear sense of public duty'' had inspired people for more than 60 years.
Despite his age Philip's decision - which was fully supported by the Queen and was not medically related - came as a surprise as he still appeared to relish meeting people and carrying out his public role.
The Duke is known for his quips and over the past few months has been joking about his impending retirement, even telling celebrity cook Prue Leith at a Palace event "I'm discovering what it's like to be on your last legs".
Buckingham Palace has stressed although the Duke's diary of engagements will come to an end on Wednesday he may decide to attend certain events, alongside the Queen, from time to time.
The Queen's public schedule continues as normal but other members of the Royal Family will step up in support of the monarch in her role as head of state.
On Wednesday, in the forecourt of Buckingham Palace Philip, in his role as Captain General of the Royal Marines, will attend a parade to mark the finale of the 1664 Global Challenge.
His association with the Royal Marines dates back 64 years to June 2, 1953 when he was appointed Captain General in succession to the late King George VI.
The challenge, which recognises the year 1664 when the Corps was founded, has seen Royal Marines all over the world raising money for the military unit's charity with a number of ingenious feats.
The 1,664 mile running challenge began in Plymouth on April 25 with Royal Marines running 16.64 miles a day for 100 days, with the gruelling trek due to end at Buckingham Palace on Wednesday.
The Duke will meet some of the runners including two Royal Marines who have completed the entire distance.
Royal Marines from around the globe have also been taking part in extreme events including a 34-mile swim underwater and a company of Royal Marines lifting more than 20,000 tonnes and running 10,000 kilometres.
During the event Philip will also meet veterans and cadets before receiving the 1664 Global Challenge baton.
The parade will end with a march past, a royal salute and three cheers for the Captain General.
Over the years Philip has attended many Royal Marines events and in 2014, to mark the Corps' 350th anniversary, the Duke wore his full ceremonial uniform as Captain General to the state opening of parliament.