A portrait of the Queen by British photographer David Bailey has been reissued for the anniversary.
In the photo, the Queen wears sapphire jewellery given to her by King George VI as a wedding gift in 1947.
The portrait was among a series taken by Bailey in 2014, with one released for the Queen's 88th birthday that year.
Prime Minister Theresa May offered her congratulations hailing the Queen as "truly an inspiration to all of us".
Meanwhile, a 41-gun salute has been fired in London's Green Park to mark the Queen's 65 years on the throne.
Gun salutes also took place in Cardiff, Edinburgh and York.
(Source : BBC News)