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Caroline of Brandenburg-Ansbach, King Christian IX of Denmark, King George II of Great Britain and Elector of Hanover, Landgrave Charles of Hesse-Cassel, Landgrave Friedrich II of Hesse-Cassel, Landgrave Friedrich of Hesse-Cassel, Landgravine of Hesse-Cassel, Louise of Hesse-Cassel, Princess Mary of Great Britain
Mary of Great Britain (March 5, 1723 – January 14, 1772) was the second-youngest daughter of King George II of Great Britain, Elector of Hanover and his wife, Caroline of Brandenburg-Ansbach, and Landgravine of Hesse-Cassel as the wife of Friedrich II, Landgrave of Hesse-Cassel.

King George II of Great Britain, Elector of Hanover
Early life
Princess Mary was born at Leicester House, Westminster, London during the reign of her grandfather King George I of Great Britain, Elector of Hanover. When she was born her father was the Prince of Wales, later King George II.
Her mother was Princess Caroline of Brandenburg-Ansbach, daughter of Johann Friedrich, Margrave of Brandenburg-Ansbach (of the House of Hohenzollern) and his second wife, Princess Eleonore Erdmuthe of Saxe-Eisenach. Her father was the ruler of one of the smallest German states; he died of smallpox at the age of 32, when Caroline was three years old.
Prince Mary’s father succeeded, as King George II of Great Britain, Elector of Hanover on June 11, 1727, and she became “HRH The Princess Mary”. Upon her death in 1737, her mother, Queen Caroline, entrusted Mary to her elder sister Caroline, urging her to “do what she could to support the meek and mild disposition of Princess Mary”.

Princess Caroline of Brandenburg-Ansbach
Marriage
A marriage was negotiated with Landgrave Friedrich of Hesse-Cassel, the only son and heir of Wilhelm VIII, Landgrave of Hesse-Cassel, and his wife Dorothea Wilhelmine of Saxe-Zeitz.
For the marriage, Parliament voted Mary £40,000.
They were married by proxy at the Chapel Royal of St. James’s Palace in London on May 8, then in person on June 28, 1740 at Cassel. They had four sons, three of whom survived to adulthood.
Princess Mary was 17 and Landgrave Friedrich was 20 at the time of their marriage.
The marriage was unhappy, and Friedrich was said to be “brutal” and “a boor”. Friedrich reportedly subjected Mary to spousal abuse. In late 1746, Mary made an extended trip to Britain to escape his maltreatment. The couple separated in 1754 on Friedrich’s conversion to Roman Catholicism. She was supported by her father-in-law, who provided her with a residence in Hanau, as she did not wish to return to Great Britain, but to stay on the continent to raise her children.

Princess Mary of Great Britain, Langravine of Hesse-Cassel
In 1756, Mary moved to Denmark, to take care of the children of her sister Louise of Great Britain, the first wife of King Frederik V of Denmark and Norway, who had died in 1751.
Princess Mary took her children with her, and they were raised at the royal court and her sons were married to Danish princesses. Her husband succeeded his father as Landgrave Friedrich II of Hesse-Cassel in 1760.
Landgrave Friedrich II of Hesse-Cassel ruled as an enlightened despot, and raised money by renting soldiers (called “Hessians”) to Great Britain to help fight the American Revolutionary War. He combined Enlightenment ideas with Christian values, cameralist plans for central control of the economy, and a militaristic approach toward international diplomacy.

Landgrave Friedrich II of Hesse-Cassel
Princess Mary was technically a Landgravine for the last twelve years of her life, despite her estrangement from her husband.
Princess Mary died on January 14 or 16, 1772, aged 48 at Hanau, in the Holy Roman Empire.
After Mary’s death her widowed husband Friedrich lost little time in marrying again. On 10 January 10, 1773, at Berlin, he married Margravine Philippine of Brandenburg-Schwed, daughter of Friedrich Wilhelm, Margrave of Brandenburg-Schwedt and Sophia Dorothea of Prussia, the ninth child and fifth daughter of King Friedrich Wilhelm I of Prussia and Sophia Dorothea of Hanover, sister of King George I of Great Britain, grandfather of Landgrave Friedrich II’s first wife Mary.
Philippine thus became stepmother to Friedrich’s three surviving sons: Wilhelm, Charles, and Friedrich. Philippine would not produce any legitimate children herself however.
During her marriage, Philippine led a widely independent life, even setting up her own court. On March 1, 1777, she gave birth to an illegitimate son, Georg Philippson, fathered by the later Württemberg statesman Georg Ernst Levin von Wintzingerode. She also helped reconcile her husband with his children from his first marriage, from whom he had been estranged since 1754.
Children and Descendants
1. Wilhelm (December 1741 – July 1, 1742)
2. Wilhelm I, Elector of Hesse (June 3, 1743 – February 27, 1821)
Originally Landgrave Wilhelm IX of Hesse-Casseland following the reorganization of the imperial states of the Holy Roman Empire during the mediatisation, called the the Reichsdeputationshauptschluss of 1803, the Landgraviate of Hesse-Cassel was raised to the Electorate of Hesse with Landgrave Wilhelm IX, now an Imperial Elector, taking the title Wilhelm I, Elector of Hesse.
3. Charles (December 19, 1744 – August 17, 1836). Brought up with relatives at the Danish court, he spent most of his life in Denmark, serving as royal governor of the twin duchies of Schleswig-Holstein from 1769 to 1836 and commander-in-chief of the Norwegian army from 1772 to 1814.

Landgrave Charles of Hesse-Cassel
On August 30, 1766 at the Christiansborg Palace Chapel, Landgrave Charles of Hesse-Cassel married his maternal first cousin, Princess Louise of Denmark and Norway who was a daughter to King Frederik V of Denmark and Norway, and his first wife Princess Louise of Great Britain (his aunt and the sister of his mother Princess Mary of Great Britain).
The marriage took place with her brother King Christian VII’s consent, despite advice given against it, due to many accusations of debauchery by Landgrave Charles and the poor influence he had on the King. This, however, did not last, as Christian VII’s warm feelings for him soon evaporated, and in the spring 1767, the couple left Copenhagen to live in Hanau.
Charles and Louise’s eldest daughter, Princess Marie of Hesse-Cassel, married her cousin King Frederik VI of Denmark.
Charles and Louise’s other daughter, Princess Louise Caroline of Hesse-Cassel, was the consort of Friedrich Wilhelm, Duke of Schleswig-Holstein-Sonderburg-Glücksburg. Amongst their children was Prince Christian who later became King Christian IX of Denmark. This made Princess Louise Caroline of Hesse-Casseland the matriarch of the House of Schleswig-Holstein-Sonderburg-Glücksburg, which became the ruling house of the kingdoms of Denmark, Greece, and Norway…and technically the United Kingdom.
4. Friedrich (September 11, 1747 – May 20, 1837). He was the last surviving legitimate grandchild of King George II of Great Britain, dying one month before Queen Victoria (granddaughter of his first cousin King George III) ascended to the throne.

Landgrave Friedrich of Hesse-Cassel
On December 2, 1786 in Biebrich, Friedrich of Hesse-Cassel married Princess Caroline of Nassau-Usingen (1762 – 1823), a remarkable heiress of a family which became extinct in the male line. 1781 he bought Rumpenheim Castle, Offenbach, from his brother Charles, and it became the family’s seat. He became known as Landgrave of Hesse-Kassel-Rumpenheim, and his descendants are known as the Hesse-Kassel-Rumpenheim branch of the House of Hesse, one of only two branches that survived to the present day.

Princess Augusta of Hesse-Cassel, Duchess of Cambridge
Friedrich and Caroline’s daughter was Princess Augusta of Hesse-Cassel (1797 – 1889) who was the wife of Prince Adolphus, Duke of Cambridge, the tenth-born child, and seventh son, of George III of the United Kingdom and Charlotte of Mecklenburg-Strelitz. The longest-lived daughter-in-law of George III, she was the maternal grandmother of Mary of Teck, wife of George V of the United Kingdom.
Friedrich and Caroline’s son, Prince Wilhelm of Hesse-Cassel
married his cousin Charlotte of Denmark (1789–1864) who was a daughter to Frederik, Hereditary Prince of Denmark and Norway, and Sophia Frederica of Mecklenburg-Schwerin.

Princess Charlotte of Denmark
They were the parents of Princess Louise of Hesse-Cassel who was the wife of Christian IX of Denmark.
King Christian IX of Denmark and Princess Louise of Hesse-Cassel were the parents of Princess Alexandra of Denmark the wife of the future King Edward VII of the United Kingdom.
Therefore, through Alexandra’s descent from Princess Mary of Great Britain and her sister Princess Louise, brings another line from King George II of Great Britain into the current British Royal Family.