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.
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.
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.
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.
Richard Wesley, 1st Baron Mornington
Richard Colley Wesley, 1st Baron Mornington (– 31 January 1758) was an Irish peer, best remembered as the grandfather of Arthur Wellesley, 1st Duke of Wellington.
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.
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.
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.
Grand Duchess Maria Nikolaevna of Russia (1819–1876)
Grand Duchess Maria Nikolaievna of Russia
(18 August 1819 – 21 February 1876) was a daughter of Emperor Nicholas I of Russia, and sister of Alexander II.
In 1839 she married Maximilian, Duke of Leuchtenberg.
She was an art collector and President of the Imperial Academy of Arts in Saint Petersburg.
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.

Question: Who is Eugen Maximilianovich, 5Th Duke Of Leuchtenberg's maternal grandfather?
Answer: Nicholas I of Russia