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 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.
Grand Duchess Elena Vladimirovna of Russia
Grand Duchess Elena Vladimirovna of Russia (17 January 1882 – 13 March 1957), sometimes known as Helen, Helena, Helene, Ellen, Yelena, Hélène, or Eleni, was a Russian grand duchess as the only daughter and youngest child of Grand Duke Vladimir Alexandrovich of Russia and Duchess Marie of Mecklenburg-Schwerin.
Her husband was Prince Nicholas of Greece and Denmark
and they were both first cousins of Emperor Nicholas II of Russia.
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 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 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 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 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.
Princess Eugénie of Greece and Denmark
Princess Eugénie of Greece and Denmark( 10 February 1910 – 13 February 1989) was the youngest child and only daughter of Prince George of Greece and Denmark and his wife, Princess Marie Bonaparte, daughter of Marie- Félix Blanc and Prince Roland Bonaparte, a great- nephew of Napoleon I.
Her father was the second son of George I of Greece and Olga Constantinovna of Russia.
As a cousin of the bridegroom, she was a leading guest at the 1947 wedding of Princess Elizabeth and Philip, Duke of Edinburgh.
She authored" Le Tsarevitch, Enfant Martyr", a biography of Aleksey Nikolaevich, Tsarevich of Russia, written in French, which was published in 1990.

Question: Who is Princess Elizabeth Of Greece And Denmark's maternal grandfather?
Answer: Grand Duke Vladimir Alexandrovich of Russia