She had been due to attend a service marking the 200th anniversary of the Most Distinguished Order of St Michael and St George.
She was due to attend St Paul's Cathedral to mark the 200th anniversary of the Order of St Michael and St George.
"Her Majesty will be represented by The Duke of Kent as Grand Master of the Order", it added.
Queen Elizabeth has pulled out of an official royal engagement last minute, on account of the 92-year-old monarch's health.
The queen has had a busy schedule in recent weeks including appearances at the Royal Ascot horse show.
Since then, he has chosen to attend some public events with The Queen, including the marriage of their grandson Prince Harry to Meghan Markle in May. The Queen remains at Buckingham Palace.
The Queen has cancelled an engagement at St Paul's Cathedral because she is ill.
The Queen was joined at the Award ceremony by the Duke and Duchess of Sussex in recognising their success.
Her final day saw her attend alongside the Duke of York, Lord Valentine Cecil and Mr. John Warren.