Maximilian Joseph Eugene Auguste Napoleon de Beauharnais, 3rd Duke of Leuchtenberg, Prince Romanowsky (2 October 1817 Munich – 1 November 1852 St.Petersburg), was the husband of Grand Duchess Maria Nikolayevna of Russia and first cousin of Emperors Napoleon III of the French and Francis Joseph I of Austria. He was a grandson of Napoleon I's first wife, the Empress Josephine, by her prior marriage to Alexandre de Beauharnais.

He was born as the second son of Eugène de Beauharnais and Princess Augusta Amalia Ludovika Georgia of Bavaria. His maternal grandparents were Maximilian I, King of Bavaria and his first wife Marie Wilhelmine Auguste, Landgravine of Hesse-Darmstadt.

His maternal grandmother Marie Wilhelmine Auguste was a daughter of Georg Wilhelm of Hesse-Darmstadt, younger son of Louis VIII, Landgrave of Hesse-Darmstadt.

He was a brother of:

His maternal grandfather Maximilian of Bavaria appointed Eugène de Beauharnais, 1st Duke of Leuchtenberg on 14 November 1817. The title came with the effective administration of the Principality of Eichstätt. Maximilian was named "Prince of Leuchtenburg" and became the second-in-line heir to the Duchy.

On 21 February 1824, his father died and his older brother became Auguste de Beauharnais, Duke of Leuchtenberg. His brother was yet childless and Maximilian became his Heir Presumptive.

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