Prince William Victor Charles Augustus Henry Sigismund of Prussia (German: Wilhelm Viktor Karl August Heinrich Sigismund; 27 November 1896 at Kiel – 14 November 1978 at Esparza, Costa Rica), was the second son of Prince Henry of Prussia and Princess Irene of Hesse and by Rhine.

They had two children:[3][1] Prior to emigrating from Europe to Central America, he served as a marine officer.

[2] In 1927, Sigismund and his family resettled in Costa Rica [4] three years after his son Alfred (1924–2013) had been born in Guatemala.

[4] In 1957, Sigismund returned to Germany to meet with Anna Anderson whom he recognized as his cousin Grand Duchess Anastasia.

In 1972, he once again reaffirmed his belief when talking to BBC journalists Anthony Summers and Tom Mangold, who were writing the File on the Tsar.