Birthday celebrations begin for Britain's Queen Elizabeth II

She will become the country's first nonagenarian monarch

Queen Elizabeth II, Britain, 90th birthday, celebrations, UK

Queen Elizabeth II leaves after officially opening a new bandstand in Windsor, as she begins her 90th birthday celebrations | Image: John Stillwell / PA Wire/Press Association Images

Britain's Queen Elizabeth II has heard what is likely to be the first of many renditions of 'Happy Birthday' after carrying out two engagements ahead of her 90th birthday.

She was greeted by hundreds of well-wishers in Alexandra Gardens, near Windsor Castle, where she opened a new bandstand.

The British monarch met school children who were involved in its decoration before they sang a number of songs, including 'When I'm 64' and 'Happy Birthday', accompanied by the Band of the Irish Guards.

The bandstand was designed in recognition of the long-standing links between the Queen, the Armed Forces and Windsor, and to mark her record as the longest-reigning monarch.

Her birthday is not until Thursday when she will become the country's first nonagenarian sovereign.

Earlier the Queen and her husband Prince Philip visited a Royal Mail delivery office to commemorate the anniversary of another British institution - the postal service.

Five hundred years ago, in 1516, Henry VIII knighted Brian Tuke, the first Master of the Posts.

Windsor delivery office manager Andy Roeton said: "There's a lot of excitement here - we're celebrating 500 years of the postal service, it's the eve of the Queen's birthday and this month I celebrate 25 years with Royal Mail".

He said of the royal visit: "I think for the staff it's recognition of the great work they do and the majority of them live in the local area - and this is one of the best things that's ever happened to me".

A series of 10 Royal Mail postage stamps marking the monarch's birthday were unveiled to coincide with the visit - with William and Catherine's son - Prince George - featuring on a stamp for the first time.