Duke Georg Alexander of Mecklenburg-Strelitz
Duke Georg Alexander of Mecklenburg-Strelitz (6 June 1859 – 5 December 1909) was the eldest of the two surviving sons of Duke Georg August of Mecklenburg-Strelitz and of Grand Duchess Catherine Mikhailovna of Russia.
He was a great-grandson of Emperor Paul and a cousin of Emperor Alexander III of Russia.
Although he was a German prince of the House of Mecklenburg-Strelitz, he was raised in Imperial Russia, where he lived all his life.
He followed a career as an officer in the Russian army and was Major General, Commander of the Life Guard Dragoon Regiment.
Georg Alexander was a music lover, a skillful cellist and composer.
In 1896 he formed a private string quartet called the "Mecklenburg Quartet".
He contracted a morganatic marriage and his rights and inheritance passed to his younger brother Charles Michael, Duke of Mecklenburg.
His four children received the title of Counts of Carlow, but after Duke Georg Alexander's death, his unmarried brother adopted his son Georg, Count of Carlow, who became the heir to the House of Mecklenburg-Strelitz in 1934.
Duchess Helene of Mecklenburg-Strelitz
Duchess Helene of Mecklenburg-Strelitz (16 January 1857 – 28 August 1936) was a daughter of Duke Georg August of Mecklenburg-Strelitz and his wife, Grand Duchess Catherine Mikhailovna of Russia.
She was the second wife of Prince Albert of Saxe-Altenburg.
Archduchess Ilona of Austria
Archduchess Ilona of Austria( 20 April 1927 – 12 January 2011) was a member of the Hungarian Palatine branch of the House of Habsburg.
She was married and later divorced from the late head of the House of Mecklenburg- Strelitz, Georg Alexander, Duke of Mecklenburg.
Grand Duchess Catherine Mikhailovna of Russia
Grand Duchess Catherine Mikhailovna of Russia  (28 August 1827 – 12 May 1894), was the third of five daughters of Grand Duke Michael Pavlovich of Russia (youngest son of Emperor
Paul I and Princess Sophie Dorothea of Württemberg) and Princess Charlotte of Württemberg (eldest child of Prince Paul of Württemberg and Princess Charlotte of Saxe-Hildburghausen).
Duchess Charlotte Georgine of Mecklenburg-Strelitz
Duchess Charlotte Georgine Luise Friederike of Mecklenburg- Strelitz( 17 November 1769 – 14 May 1818) was a member of the House of Mecklenburg- Strelitz and a Duchess of Mecklenburg- Strelitz by birth and a Duchess of Saxe- Hildburghausen through her marriage to Frederick, Duke of Saxe- Hildburghausen( later Duke of Saxe- Altenburg).
Princess Augusta of Cambridge
Princess Augusta of Cambridge( 19 July 1822 – 5 December 1916) was a member of the British Royal Family, a granddaughter of George III.
She married into the Grand Ducal House of Mecklenburg- Strelitz and became the Grand Duchess of Mecklenburg- Strelitz.
Duke Carl Gregor of Mecklenburg
Carl Gregor Duke of Mecklenburg( 14 March 1933 – 23 July 2018) was a member of the House of Mecklenburg- Strelitz and a music and art historian.
Georg Alexander, Duke of Mecklenburg
Georg Alexander, Duke of Mecklenburg( 27 August 1921 – 26 January 1996) was the head of the House of Mecklenburg- Strelitz from 1963 until his death.
Princess Elisabeth of Anhalt
Princess Elisabeth of Anhalt (7 September 1857 – 20 July 1933) was the Grand Duchess of Mecklenburg-Strelitz from 1904 to 1914 as the spouse of Adolf Friedrich V, Grand Duke of Mecklenburg-Strelitz.
Duke Georg August of Mecklenburg-Strelitz
Georg August( 11 January 1824 – 20 June 1876) was a member of the House of Mecklenburg- Strelitz and titular duke of Mecklenburg- Strelitz.

Question: Who is Duke Georg Alexander Of Mecklenburg-Strelitz's maternal grandfather?
Answer: Grand Duke Michael Pavlovich of Russia