There will be no public celebrations as the monarch continues to observe two weeks of mourning until Friday.
No photograph celebrating the day is expected to be released this year, as is customary.
Some of the Queen’s family are thought to be with her in Windsor, as well as around 20 staff, dubbed HMS Bubble.
The duke was nine weeks away from his 100th birthday, which was due to be the focus of royal celebrations this year – with the Queen’s 95th a more pared-back affair.
The Queen became the world’s oldest monarch in 2015.
Her official birthday in June is marked by the Trooping of the Colour parade, which has been cancelled for a second consecutive year because of the coronavirus pandemic.
Buckingham Palace said options for a parade in the quadrangle at Windsor Castle are being considered instead.