The former King of Spain, King Juan Carlos I, celebrates his 84th birthday today. Juan Carlos reigned over Spain from 1975 until 2014, when he abdicated in favour of his son, the current King Felipe VI of Spain. Spain is one of a few European countries to still have a monarchy, and the Spanish royal family has links to the British Royal Family, too.

       Queen Elizabeth II is a descendant of Queen Victoria and King Christian IX of Denmark.

       As the daughter of the late King George VI, Queen Elizabeth II is the great-great-granddaughter of Queen Victoria through her paternal family.

       King Christian IX of Denmark's daughter Princess Alexandra married Queen Victoria's eldest son Prince Edward, and they would become King Edward VII and Queen Alexandra of the United Kingdom.

       Through this union, Queen Elizabeth II is the great-great-granddaughter of King Christian IX of Denmark as well.

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       The former King Juan Carlos I of Spain is distantly related to Queen Elizabeth II, like many monarchs across Europe.

       Juan Carlos I is also a descendant of Queen Victoria, as the son of Infante Juan, Count of Barcelona, who was the son of Victoria Eugenie of Battenberg.

       Victoria Eugenie of Battenberg was the daughter of Princess Beatrice, Queen Victoria's youngest child.

       King Juan Carlos I is married to the former Queen Sofia of Spain, who was born Princess Sophia of Greece and Denmark.

       Due to his mother and father's lineage, Juan Carlos and Sofia's son, the current King Felipe VI of Spain, is a descendant of both Queen Victoria and Christian IX of Denmark.

       Queen Sofia's father was King Paul of Greece - his father was King Constantine I of Greece, and his grandfather was King George I of Greece.

       King George I of Greece was the son of King Christian IX of Denmark.

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       And Queen Sofia's grandmother, Sophia of Prussia, was the daughter of Princess Victoria, Queen Victoria's eldest child.

       Therefore, through several ancestral connections, King Juan Carlos I and King Felipe VI of Spain are distantly related to Queen Elizabeth II and the British Royal Family.

       King Felipe VI of Spain wrote a personal message to the Queen following the death of Prince Philip last year, in which he called the monarch by a touching familial name.

       He wrote: ”Dear Aunt Lillibet, we are deeply saddened to hear about the passing away of dear uncle Philip.

       "In these sad moments, we would like to send you our most heartfelt condolences on behalf of the government and people of Spain, and all our sympathy and support."