Question: Who is Olga Constantinovna Of Russia's maternal grandfather?

Knowledge 1: Olga Constantinovna of Russia
Olga Constantinovna of Russia (18 June 1926) was Queen consort of the Hellenes as the wife of King George I.She was briefly the regent of Greece in 1920.A member of the Romanov dynasty, she was the daughter of Grand Duke Constantine Nikolaievich and his wife, Princess Alexandra of Saxe-Altenburg.She spent her childhood in Saint Petersburg, Poland and the Crimea, and married King George I of Greece in 1867 at the age of sixteen.At first, she felt ill at ease in the Kingdom of Greece, but she quickly became involved in social and charitable work.She founded hospitals and schools, but her attempt to promote a new, more accessible, Greek translation of the Gospels sparked riots by religious conservatives.On the assassination of her husband in 1913, Olga returned to Russia.When the First World War broke out, she set up a military hospital in Pavlovsk Palace, which belonged to her brother.She was trapped in the palace after the Russian Revolution of 1917, until the Danish embassy intervened, allowing her to escape to Switzerland.Olga could not return to Greece as her son, King Constantine I, had been deposed.In October 1920, she returned to Athens on the fatal illness of her grandson, King Alexander.After his death, she was appointed regent until the restoration of Constantine I the following month.After the defeat of the Greeks in the Greco-Turkish War of 1919–22the Greek royal family were again exiled and Olga spent the last years of her life in the United Kingdom, France and Italy. [SEP] Knowledge 2: Princess Alexandra of Saxe-Altenburg
Grand Duchess Alexandra Iosifovna of Russia (8 July 1830 – 6 July 1911), born Princess Alexandra Friederike Henriette of Saxe-Altenburg, was the fifth daughter of Joseph, Duke of Saxe-Altenburg and Amelie Theresa Luise, Duchess of Württemberg.She is an ancestor of the British, Greek, Romanian, Yugoslavian and Spanish Royal Families through her elder daughter Olga.
Knowledge 1: Olga Constantinovna of Russia
Olga Constantinovna of Russia (18 June 1926) was Queen consort of the Hellenes as the wife of King George I.She was briefly the regent of Greece in 1920.A member of the Romanov dynasty, she was the daughter of Grand Duke Constantine Nikolaievich and his wife, Princess Alexandra of Saxe-Altenburg.She spent her childhood in Saint Petersburg, Poland and the Crimea, and married King George I of Greece in 1867 at the age of sixteen.At first, she felt ill at ease in the Kingdom of Greece, but she quickly became involved in social and charitable work.She founded hospitals and schools, but her attempt to promote a new, more accessible, Greek translation of the Gospels sparked riots by religious conservatives.On the assassination of her husband in 1913, Olga returned to Russia.When the First World War broke out, she set up a military hospital in Pavlovsk Palace, which belonged to her brother.She was trapped in the palace after the Russian Revolution of 1917, until the Danish embassy intervened, allowing her to escape to Switzerland.Olga could not return to Greece as her son, King Constantine I, had been deposed.In October 1920, she returned to Athens on the fatal illness of her grandson, King Alexander.After his death, she was appointed regent until the restoration of Constantine I the following month.After the defeat of the Greeks in the Greco-Turkish War of 1919–22the Greek royal family were again exiled and Olga spent the last years of her life in the United Kingdom, France and Italy. [SEP] Knowledge 2: Abdul-Vahed Niyazov
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Knowledge 1: Olga Constantinovna of Russia
Olga Constantinovna of Russia (18 June 1926) was Queen consort of the Hellenes as the wife of King George I.She was briefly the regent of Greece in 1920.A member of the Romanov dynasty, she was the daughter of Grand Duke Constantine Nikolaievich and his wife, Princess Alexandra of Saxe-Altenburg.She spent her childhood in Saint Petersburg, Poland and the Crimea, and married King George I of Greece in 1867 at the age of sixteen.At first, she felt ill at ease in the Kingdom of Greece, but she quickly became involved in social and charitable work.She founded hospitals and schools, but her attempt to promote a new, more accessible, Greek translation of the Gospels sparked riots by religious conservatives.On the assassination of her husband in 1913, Olga returned to Russia.When the First World War broke out, she set up a military hospital in Pavlovsk Palace, which belonged to her brother.She was trapped in the palace after the Russian Revolution of 1917, until the Danish embassy intervened, allowing her to escape to Switzerland.Olga could not return to Greece as her son, King Constantine I, had been deposed.In October 1920, she returned to Athens on the fatal illness of her grandson, King Alexander.After his death, she was appointed regent until the restoration of Constantine I the following month.After the defeat of the Greeks in the Greco-Turkish War of 1919–22the Greek royal family were again exiled and Olga spent the last years of her life in the United Kingdom, France and Italy. [SEP] Knowledge 2: Kaya Alp
Kaya Alp was, according to Ottoman tradition, the son of Kızıl Buğa and the father of Suleyman Shah, who was, in turn, the grandfather of Ertuğrul, and the great grandfather of the Ottoman Empire founder, Osman I.

Answer: Joseph, Duke of Saxe-Altenburg