| Birth Date: | 21 May 1822 |
| Birth Place: | Soestdijk Palace, Baarn, United Kingdom of the Netherlands |
| Death Date: | |
| Death Place: | Brussels, United Kingdom of the Netherlands |
| Burial Place: | Nieuwe Kerk, Delft |
| Full Name: | William Alexander Frederick Ernest Casimir |
| House: | Orange-Nassau |
| Father: | William II of the Netherlands |
| Mother: | Grand Duchess Anna Pavlovna of Russia |
Prince William Alexander Frederick Ernest Casimir of the Netherlands, Prince of Orange-Nassau (Dutch: Willem Alexander Frederik Ernst Casimir, Prins der Nederlanden, Prins van Oranje-Nassau; Soestdijk Palace, 21 May 1822 – Brussels, 22 October 1822) was the fourth son of the Prince of Orange, later King William II of the Netherlands and his wife Grand Duchess Anna Pavlovna of Russia.
He was baptized on 18 June 1822 in the Nieuwe Kerk, Amsterdam. However, because he had hydrocephalus, he died the same year. He was buried in the Protestant Church in Brussels until his body was transferred to the Royal Crypt in the Nieuwe Kerk, Delft, in 1860.