Elisabeth of Oettingen
Elisabeth of Oettingen also known as" Elizabeth of Leuchtenberg"( born:; died: 9 July 1406) was a member of the House of Oettingen- Wallerstein by birth.
She was a Landgravine of Leuchtenberg by marriage and a lady in waiting for Elector Palatine and King of Germany Rupert.
George Maximilianovich, 6th Duke of Leuchtenberg
Prince George Maximilianovich Romanowsky, 6th Duke of Leuchtenberg (29 February 1852 – 16 May 1912), also known as Prince Georgii Romanovsky or Georges de Beauharnais, was the youngest son of Maximilian de Beauharnais, 3rd Duke of Leuchtenberg and his wife, Grand Duchess Maria Nikolaevna of Russia.
Gregorio María de Silva y Mendoza, 9th Duke of the Infantado
Gregorio de Silva y Mendoza( born 1649, Pastrana- d. 1693, Madrid) was a Spanish noble from the House of Mendoza.
He was the 5th Duke of Pastrana 9th Duke of the Infantado, 7th Duke of Lerma, 6th Duke of Francavilla, 5th Duke of Estremera, and the Prince of Eboli and Melito.
Eugen Maximilianovich, 5th Duke of Leuchtenberg
Eugen Maximilianovich Romanowsky, 5th Duke of Leuchtenberg, Prince Romanowsky (8 February 1847 – 31 August 1901) was a son of Maximilian de Beauharnais, 3rd Duke of Leuchtenberg and Grand Duchess Maria Nikolaevna of Russia Duke of Leuchtenberg.
He succeeded his brother Nicholas Maximilianovich as Duke of Leuchtenberg from 1891 until his death.
Charles Gordon-Lennox, 7th Duke of Richmond
Charles Henry Gordon- Lennox, 7th Duke of Richmond and Lennox, 2nd Duke of Gordon,( 27 December 1845 – 18 January 1928), 7th Duke of Aubigny( French peerage in the French nobility), styled Lord Settrington until 1860 and Earl of March between 1860 and 1903, was a British politician and peer.
Auguste, Duke of Leuchtenberg
Auguste Charles Eugène Napoléon, Duke of Leuchtenberg( 9 December 1810 – 28 March 1835) was the first prince consort of Maria II of Portugal.
Besides being the 2nd Duke of Leuchtenberg and 2nd Prince of Eichstätt, he also held the Brazilian noble title of Duke of Santa Cruz.
Alexander Georgievich, 7th Duke of Leuchtenberg
Alexander Georgievich, 7th Duke of Leuchtenberg, also known as Prince Alexander Georgievich Romanovsky or less commonly Alexander de Beauharnais (13 November 1881 – 26 September 1942) was the only son of George Maximilianovich, 6th Duke of Leuchtenberg by his first wife Duchess Therese of Oldenburg.
He was a descendant of Paul I of Russia from both of his parents.
Sergei Georgievich, 8th Duke of Leuchtenberg
Prince Sergei Georgievich Romanowsky, 8th Duke of Leuchtenberg (4 July 1890 – 7 January 1974) was the son of Prince George Maximilianovich Romanowsky, 6th Duke of Leuchtenberg and his second wife Princess Anastasia of Montenegro.
He succeeded his half-brother Alexander Georgievich as Duke of Leuchtenberg from 1942 until his death.
Alexander Hamilton, 10th Duke of Hamilton
Alexander Hamilton, 10th Duke of Hamilton, 7th Duke of Brandon KG PC FRS FSA (3 October 1767 – 18 August 1852) was a Scottish politician and art collector.
Countess Elisabeth of Leuchtenberg
Elisabeth of Leuchtenberg( born: March 1537- died: 6 July 1579 in Dillenburg) was the daughter of Landgrave George III, Landgrave of Leuchtenberg and Margravine Barbara of Brandenburg- Ansbach.

Question: Who is the paternal grandfather of Alexander Georgievich, 7Th Duke Of Leuchtenberg?
Answer: Maximilian de Beauharnais, 3rd Duke of Leuchtenberg