At 13, the future Queen first met a then 18-year-old Prince Philip when she joined her parents and sister Princess Margaret on a 1939 visit to Dartmouth naval college.
Taking part in the procession in the grounds will bring back some memories of the funeral of Diana, Princess of Wales for William, who was just 15 when he walked behind his mother's coffin through central London after her death in a vehicle crash in 1997.
Donatus and Philipp were seen arriving at Windsor together in a auto, both wearing black face masks and suits, as were all the other royals.
Coronavirus restrictions mean that instead of the 800 mourners included in the longstanding plans for his funeral, there will be only 30 inside the castle's St. George's Chapel, including the widowed queen, her four children and her eight grandchildren.
The duke was intimately involved in planning his own funeral service, selecting the music and making sure the ceremony reflects his military affiliations and personal interests. The ceremony is due to last around 50 minutes.
Only Queen Elizabeth and members of Prince Philip's family have been invited to attend - leaving notable names like Prime Minister Boris Johnson off the guest list. Among the readings will be Ecclesiasticus 43 and John 11.
The Duke of York, 61, will make his first appearance at an official royal event since exiting the royal frontline in 2019, after he gave a disastrous TV interview about his friendship with convicted sex offender Jeffrey Epstein. "It also avoids the worries that the government have over people congregating during the time of the pandemic", royal expert Omid Scobie told ET.
Full details of the order of service are to be released later in the week, but there will be a small choir of four singers. When the Queen dies, he will be transferred to the King George VI memorial chapel to lie next to her.
Prince Philip’s funeral takes place in Windsor today
The funeral is set to start at the end of the minute's silence.
On Saturday morning, Philip's coffin will be moved via a Bearer Party founded by The Queen's Company, 1st Battalion Grenadier Guards, and "positioned in the Quadrangle at Windsor Castle there will be representative detachments drawn from His Royal Highness's military special relationships".
The last major royal funeral - of the Queen´s mother, also called Queen Elizabeth - in 2002 cost more than Â£5.4 million ($7.4 million) and saw more than one million people throng outside Westminster Abbey in central London.
William's former university flatmate turned future Queen adapted to her royal role easily after her wedding, and has attended many solemn memorials and commemorations, including Remembrance Sunday events and a service to mark the end of combat operations in Afghanistan.