A glittering night of European monarchs celebrating the Queen's Golden Jubilee will not simply be a formal regal affair.
As well as the pomp and ceremony many of the guests share blood ties, constitutional and historical similarities and modern day crises with the Queen.
Among the Royal Who's Who of Europe will be at least four of the Queen's distant cousins.
Several are direct descendants of Queen Victoria, including Danish Queen Margrethe, Norway's King Harald and Sweden's King Carl XVI Gustaf.
Another direct descendent is prince Ernst August of Hanover who, had Britain operated a men-only law of succession, could have been sitting on the throne in Buckingham Palace today.
The Queen has also invited King Albert of Belgium, Queen Beatrix of the Netherlands King Carl VII Gustaf of Sweden and King Juan Carlos of Spain.
The long standing relationship between the Queen and her European counterparts began in childhood.
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The Queen Mother, the then Queen, accommodated and entertained various fleeing European leaders during World War II.
In modern times, the Queen is the longest serving monarch and as such she is regarded as the senior member of the group.
But there is much in common between some of the royals which share the same robust and traditional monarchy as Britain - such as the Swedes and the Danes.
They both have a similar constitutional monarchy as the UK.
In Denmark, Queen Margrethe II came to be head of state in 1972, 20 years after the Queen.
Queen Margrethe and the Queen, 14 years her senior, still address each other in public as "your majesty" despite being cousins, but in private they are close friends.
Other monarchies are still in their infancy, such as Belgium, which is only about a century old, and Norway, which dates back to 1905 when it became independent from Sweden.
Across Europe the media and public have been as scathing and fascinated by events in the royals' private lives as here in Britain.
In Denmark there was much scandal when the Danish Queen's husband, Prince Consort Henrik, fled Denmark earlier this year for his native France after he said his public role had been downgraded.
Changing times
It came after the couple's son, Crown Prince Frederik, was given higher status than him in the monarchy.
The 67-year-old complained that in 35 years of marriage the Danish nation had never accepted him - he finally returned three weeks later.
Until the 20th century marriage outside royal circles was extremely rare, and outside the non-Christian ancestry it was unheard of. But things have changed.
In Norway, the marriage of Crown Prince Haakon to a commoner and single-mother, Mette-Marit Tjessem Hoiby, caused concern.
As did his sister's marriage, Princess Martha Louise to Ari Behn.
Her groom controversially made a television programme showing prostitutes taking cocaine in Las Vegas.
An estimated 52% of the 4.5m people wanted a referendum on the monarchy following some of the marriage revelations.
Similar tales come from the Netherlands when Dutch Crown Prince Willem-Alexander, 34, announced his engagement to Maxima Zorreguieta, 30.
She is the daughter of Jorge Zorreguieta, who was a minister in Argentina's brutal military dictatorship of Jorge Videla.
At the height of controversy there was speculation he could not be king.
Despite the gossip and speculation the monarchies remain strong, which may give them more on a personal note to celebrate and look forward to as they toast the Queen's 50 years on the throne.
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