The Queen celebrated her Sapphire Jubilee on Monday, marking 65 years on the British throne.

She became the UK’s longest-reigning monarch in 2015, when she surpassed her great great grandmother Queen Victoria. Aged 90, the Queen is now the first British monarch to reach their Sapphire Jubilee.

The King’s Troop Royal Horse Artillery fired a 41-gun salute was fired in London’s Green Park to commemorate the occasion. Salutes also took place in Cardiff, Edinburgh and York.

Prime Minister Theresa May congratulated the Queen, hailing her as ‘truly an inspiration to all of us.’

Mrs May said: “I know the nation will join with me today in celebrating and giving thanks for the lifetime of service Her Majesty the Queen has given to our country and to the Commonwealth.”

65th Year and Still Going Strong 👸🏼 #sapphirejubilee #queenelizabeth #keepcalmandcarryon https://t.co/tQjna6MEcn

— ♔Rebecca Jane♔ (@R_Jane01) February 8, 2017

The sapphire anniversary is officially known as Accession Day. The Queen will spend it in private at her Sandringham Estate, in Norfolk, withdrawing from public view and abstaining from any public engagements.

British photographer David Bailey had received a commission to retake a portrait of the Queen, originally issued for her 88^th birthday, for the anniversary.

I have the honour to remain, madam, your majesty’s most humble and obedient servant #SapphireJubilee pic.twitter.com/MA6MT6ACQI

— Yaz Alahdal (@yazeedalahdal) February 7, 2017

Grand jubilee celebrations are expected to take place in 2022, the Queen’s Platinum Jubilee, recording her 70^th year on the British throne.

It is perhaps a moment for reflection rather than celebration as the day of the Queen’s Sapphire Jubilee also marked the anniversary of the death of her father, King George VI, on February 6 1952.

“This will be a day for quiet reflection for Her Majesty, not celebration. One must remember, the moment she became Queen marks the moment her beloved father passed away,” a senior royal aide said.

Queen Elizabeth II was the first child of the Duke and Duchess of York. Born in 1926, she is the 41^st monarch since William the Conquer seized the Crown in 1066.

She was third in line to the throne and was not expected to be Queen. Her status as heir happened when her uncle, Edward VIII, abdicated in 1936 and her father, George VI, acceded the British throne.

In 2015, upon becoming the longest-reigning monarch in British history, the Queen said: “Initially, a long life can pass by many milestones. My own is no exception.”

Following the death of King Bhumibol Adulyadej of Thailand in 2016, the Queen is now also the longest-reigning monarch in the world.

In order to commemorate Her Majesty’s 65^th anniversary, the Royal Mint issued specially designed Sapphire Jubilee coins and the Royal Mail- a Sapphire Jubilee five pound stamp.

The Queen has yet to celebrate more forthcoming special occasions. In November, she and Prince Philip will mark 70 years of marriage.