The Royal Family will come together today to mark the Duke of Edinburgh's 90th birthday at a special service of thanksgiving.
The Queen and the rest of the royals will officially celebrate the nonagenarian patriarch's milestone age at Windsor Castle's St George's Chapel.
More than 750 guests including the newlywed Duke and Duchess of Cambridge and Prince Harry are to attend the traditional religious service in the 15th century gothic church in Philip's honour.
Representatives from the sailing, polo, carriage driving and shooting worlds will also join foreign royals, members of the Mountbatten family, the Duke's godchildren and former and present staff from the Royal Household in the congregation.
The Queen and Philip's four children - the Prince of Wales, the Princess Royal, the Duke of York and the Earl of Wessex - will be there in tribute, as will the royal couple's older grandchildren and extended family.
Following a canapes reception for guests afterwards in the castle's impressive St George's Hall and Grand Reception Room, the royals will sit down for a private family celebratory lunch.
Philip, who turned 90 on Friday, is intent on keeping his birthday weekend low key.
He treated Friday as a normal working day, hosting a Palace reception for the 100th anniversary of the Royal National Institute for Deaf People - now rebranded as Action On Hearing Loss.
Even today's service in the chapel, led by the Dean of Windsor the Right Reverend David Conner, will take place away from the spotlight with no media permitted inside nor members of the public allowed in the Lower Ward of the castle.
One aide said: "That's the way he likes it. It's low key. It's very typical of him."
On his birthday, Philip was made Lord High Admiral of the Royal Navy by the Queen - a title she had held herself for 37 years.
It was perhaps a touching acknowledgement of the sacrifices he has made for his wife.
Philip gave up his promising naval career to devote his life to royal duty and support the Queen in her role as sovereign.
Roads around Windsor will be closed today for the 21st Toshiba Windsor Triathlon, with more than 2,400 competitors taking part in the Berkshire race.