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 Sophie of Greece and Denmark
Princess Sophie of Greece and Denmark( 26 June 1914 – 24 November 2001) was the fourth child and youngest daughter of Prince Andrew of Greece and Denmark and Princess Alice of Battenberg.
The Duke of Edinburgh is her younger brother.
Sophie was born at the villa Mon Repos on the island of Corfu in Greece.
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 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".
Helen of Greece and Denmark
Helen of Greece and Denmark ("Eleni"; ; 2 May 1896 – 28 November 1982), was the queen mother of Romania during the reign of her son King Michael (1940–1947).
She was noted for her humanitarian efforts to save Romanian Jews during World War II, which led to her being awarded by the State of Israel with the honorific of "Righteous Among the Nations" in 1993.
Daughter of King Constantine I of Greece and his wife, Princess Sophia of Prussia, Princess Helen spent her childhood in Greece, Great Britain and Germany.
The outbreak of World War I and the overthrow of her father by the Allies in 1917 permanently marked her and also separated her from her favorite brother, the young Alexander I of Greece.
Exiled in Switzerland along with most members of the royal family, Helen then spent several months caring for her father, plagued by disease and depression.
In 1920, the princess met Carol, Crown Prince of Romania, who quickly asked her hand in marriage.
Despite the bad reputation of the prince, Helen accepted and moved to Romania, where she soon gave birth to their only son, Prince Michael, in 1921.
The situation of her family, however, continued to worry Helen, who made several trips abroad to visit her parents when they did not simply reside with her in Bucharest.
In doing this, she distanced herself from her husband, whose multiple affairs ended when he fell in love with Magda Lupescu in 1924.
Finally, in 1925, Prince Carol abandoned his wife and renounced the throne in order to live openly with his mistress.
Distraught, Helen tried to persuade her husband to return to her
but eventually she accepted the divorce in 1928.
In the meanwhile, Helen was proclaimed "Queen Mother of Romania" in 1927, as her son Michael ascended to the throne under the regency of his uncle Prince Nicholas.
However, the political situation in Romania was complicated and Carol took advantage of the increased instability to return to Bucharest in 1930 and be acclaimed as king.
Soon, the new ruler forced his ex-wife into exile and only authorized her to see their son two months per year.
In these circumstances, Helen moved to Villa Sparta at Fiesole, Tuscany.
Always close to her family, she hosted her sisters Irene and Katherine and brother Paul, who stayed with her intermittently until the restoration of the Greek monarchy in 1935.
The outbreak of World War II, the deposition of Carol II and the subsequent dismemberment of Greater Romania in 1940, however, brought Helen back to be with her son in Bucharest.
Subject to the dictatorship of General Antonescu and vigilance of Nazi Germany, the king and his mother were cautious in their dealings with the fascist regime.
They did not show their opposition to the participation of Romania in the invasion of the Soviet Union and the deportation of Jews.
Finally, King Michael organized a coup against Antonescu on 23 August 1944 and Romania turned against the Axis powers; however, the country was, in the end, occupied by the Red Army.
For Helen and her son, the post-war period was marked by the interference of the Soviet Union in the Romanian political life.
In March 1945, the king was forced to accept a communist government headed by Petru Groza while the following year, the general elections confirmed the hegemony of the PCR in the country.
Finally, Michael I was forced to abdicate on 30 December 1947 and the royal family took the path of exile.
Helen then returned to the Villa Sparta, where she divided her time among her family, gardening and the study of Italian art.
Increasingly concerned about her finances, Helen finally left Italy for Switzerland in 1979 and died three years later with her son at her side.
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 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 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.
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.

Question: What is the cause of death of Helen Of Greece And Denmark's mother?
Answer: cancer