But there is one family member who may not be able to fly back to the UK to join in the festivities – the Duchess of Sussex.
Meghan, who announced her pregnancy on Valentine's Day, is thought to be around five months pregnant, which would put her due date around June.
WATCH: All the hints that Meghan Markle was expecting another baby
Her Majesty turns 95 in April but traditionally holds her birthday parade, also known as Trooping the Colour, in mid-June. The royals were not able to celebrate last year because of lockdown and for the public's safety; the military parade along the Mall usually attracts thousands of spectators.
Meanwhile, Prince Philip's milestone birthday falls on 10 June.
The Queen's official birthday celebration falls in June
Given Meghan's suspected June due date, it is unlikely the Duchess – who will be heavily pregnant at the time or may even have given birth – will be flying long distance, even if travel restrictions are lifted.
It's likely that Prince Harry, however, will leave his wife and children behind to carry out a whirlwind visit to the UK, to celebrate the birthdays of his grandparents who he is so close to. Shortly after Archie's birth in 2019, the Duke undertook a fleeting visit to The Netherlands for the Invictus Games.
The Duchess is expected to give birth in June
Harry and Meghan live in Santa Barbara, California with their one-year-old son Archie. The couple are expected to be based there for the foreseeable future and Meghan may choose to give birth at Cedars-Sinai Medical Centre in Los Angeles – the maternity ward of the stars.
Kim Kardashian, Victoria Beckham, Britney Spears, Kate Hudson and Jessica Simpson are among the celebrity mums who have delivered their children in the deluxe maternity ward.
The Duchess could make use of the hospital's secret entrances so that she won't be photographed arriving or leaving. New mothers are also given welcome packs which include nappies and a miniature bottle of wine, while gourmet cuisine is also on offer. The hospital's deluxe maternity suite package costs thousands of pounds a night and includes a three-room suite, as well as the assistance of a doula.
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