Princess Irene of Greece and Denmark
Princess Irene of Greece and Denmark( born 11 May 1942) is the youngest child and second daughter of King Paul of Greece and his wife Princess Frederika of Hanover.
She is the younger sister of Queen Sofía of Spain and of the deposed King Constantine II of Greece and maternal aunt of Felipe VI of Spain.
Princess Elizabeth of Greece and Denmark
Princess Elisabeth of Greece and Denmark( 24 May 1904 – 11 January 1955) was the middle daughter of Prince Nicholas of Greece and Grand Duchess Elena Vladimirovna of Russia.
Princess Xenia Georgievna of Russia
Princess Xenia Georgievna of Russia( 22 August 1903, Mikhailovskoe, Russia – 17 September 1965, Glen Cove, New York) was the younger daughter of Grand Duke George Mihailovich of Russia and Princess Maria Georgievna of Greece and Denmark.
She was a granddaughter of George I of Greece and first cousin of the brothers King Alexander I of Greece, King George II of Greece, King Paul I of Greece and their sister Queen Helen, Queen Mother of Romania and also of Prince Philip, Duke of Edinburgh.
Princess Katherine of Greece and Denmark
Princess Katherine of Greece and Denmark (4 May 1913 – 2 October 2007), styled in the UK as Lady Katherine Brandram from 1947 till her death, was the third daughter and youngest child of King Constantine I of Greece and Sophia of Prussia.
Princess Margarita of Greece and Denmark
Princess Margarita of Greece and Denmark( 18 April 1905 – 24 April 1981) was the eldest child and daughter of Prince Andrew of Greece and Denmark and Princess Alice of Battenberg.
She was the first great- great- grandchild of Queen Victoria, and the eldest sister of Prince Philip, Duke of Edinburgh.
Princess Anastasia of Greece and Denmark
Princess Anastasia of Greece and Denmark ("née" Nonie May Stewart; 20 January 1878 – 29 August 1923) was an American-born heiress and member of the Greek Royal Family.
She was married to Prince Christopher of Greece and Denmark, the youngest child of King George I of Greece and his consort, Grand Duchess Olga Constantinovna of Russia, but was created a princess "suo jure".
Princess Irene, Duchess of Aosta
Princess Irene of Greece and Denmark( 13 February 1904 – 15 April 1974) was the fifth child and second daughter of Constantine I of Greece and his wife, the former Princess Sophie of Prussia.
She was a member of the royal families of Greece and Italy.
From 1941 to 1943 she was also officially Queen Consort of Croatia.
Sophia of Prussia
Sophia of Prussia ("Sophia Dorothea Ulrike Alice"; 14 June 1870 – 13 January 1932) was Queen consort of Greece during 1913–1917 and 1920–1922.
A member of the House of Hohenzollern and daughter of Frederick III, German Emperor, Sophia received a liberal and anglophile education, under the supervision of her mother, Victoria, Princess Royal.
In 1889, less than a year after the death of her father, she married her third cousin Constantine, heir apparent to the Greek throne.
After a difficult period of adaptation in her new country, Sophia gave birth to six children and became involved in the assistance to the poor, following in the footsteps of her mother-in-law, Queen Olga.
However, it was during the wars which Greece faced during the end of the 19th and the beginning of the 20th century that Sophia showed the most social activity: she founded field hospitals, oversaw the training of Greek nurses, and healed wounded soldiers.
However, Sophia was hardly rewarded for her actions, even after her grandmother Queen Victoria decorated her with the Royal Red Cross after the Thirty Days' War: the Greeks criticized her links with Germany.
Her brother Emperor William II was indeed an ally of the Ottoman Empire and openly opposed the construction of the "Megali Idea", which could establish a Greek state that would encompass all ethnic Greek-inhabited areas.
During World War I, the blood ties between Sophia and the German Emperor also aroused the suspicion of the Triple Entente, which criticized Constantine I for his neutrality in the conflict.
After imposing a blockade of Greece and supporting the rebel government of Eleftherios Venizelos, causing the National Schism, France and its allies deposed Constantine I in June 1917.
Sophia and her family then went into exile in Switzerland, while the second son of the royal couple replaced his father on the throne under the name of Alexander I.
At the same time, Greece entered the war alongside the Triple Entente, which allowed it to grow considerably.
After the outbreak of the Greco-Turkish War in 1919 and the untimely death of Alexander I the following year, the Venizelists abandoned power, allowing the royal family's return to Athens.
The defeat of the Greek army against the Turkish troops of Mustafa Kemal, however, forced Constantine I to abdicate in favor of his eldest son George II in 1922.
Sophia and her family then were forced to a new exile, and settled in Italy, where Constantine died one year later (1923).
With the proclamation of the Republic in Athens (1924)
Sophia spent her last years alongside her family and died of cancer in Germany in 1932.
Princess Theodora of Greece and Denmark (1906–1969)
Princess Theodora of Greece and Denmark( 30 May 1906 – 16 October 1969) was the second child and daughter of Prince Andrew of Greece and Denmark and Princess Alice of Battenberg, and the second eldest sister of Prince Philip, Duke of Edinburgh.
Richard Brandram
Richard Campbell Andrew Brandram, MC( 5 August 1911 – 28 March 1994) was a Major in the British Army who married Princess Katherine of Greece and Denmark in 1947, which united him with most of the royal families in Europe.

Question: Why did Princess Katherine Of Greece And Denmark's mother die?
Answer: cancer