Eugen Maximilianovich was born in Saint Petersburg in 1847, as the second son and fifth child of Maximilian de Beauharnais, 3rd Duke of Leuchtenberg and Grand Duchess Maria Nikolaevna of Russia.

After the death of his father in 1852, Eugen's older brother Nicolas became the fourth Duke of Leuchtenberg.

On 18 December 1852, after the death of their father, all the children of Duke Maximilian were allowed to wear the princely name and title of Romanowsky (or Romanovskaya for the female descendants), and were styled Imperial Highness.

[1] In 1869, he married Daria Konstantinova Opochinina, the granddaughter of Mikhail Kutuzov: she was made Countess of Beauharnais (died 1870 in childbirth).

Zina later had an open long-term affair with Grand Duke Alexei Alexandrovich of Russia.