However, Her Majesty was joined for the day of RAF Centenary celebrations by the rest of the Royal Family.
While many expected Prince Charles to walk his mother to his seat, the 92-year-old made her way down the aisle on her own, just behind Charles and Camilla.
The Duke and Duchess will also visit DogPatch Labs, a co-working space for technology start-ups, where they will meet children and young people taking part in workshops, and talk to female tech entrepreneurs. Prince William formerly served as an RAF search and rescue pilot, while Prince Harry received helicopter training from the RAF during his time in the Army Air Corps. Five years ago, Prince George was christened there, and before her wedding day in April 2011, the Duchess of Cambridge received her first communion there when she was confirmed to the Church of England.
The Duchess of Cambridge wore a McQueen cream dress and white floral headpiece by Jane Taylor.
Queen Elizabeth and senior members of her family were attending celebrations to mark the 100th anniversary of Britain's Royal Air Force on Tuesday, ahead of a flypast of nearly 100 aircraft over Buckingham Palace in central London. Following the service at Westminster, a royal flypast took place over Buckingham Palace.
Also joining the monarch will be Prince Charles and Camilla as well as Prince William and Kate for the RAF event on July 10.