Justinus van Nassau (1559–1631) was the only extramarital child of William the Silent.

He was a Dutch army commander known for his role in the defeat of the Spanish Armada, his leadership of the forces in Breda during the siege of 1624, and the depiction of his surrender in the painting by Diego Velázquez, The Surrender of Breda.

On 28 February 1585 he became lieutenant-admiral of Zeeland, and fought in 1588 against the Spanish Armada, capturing two galleons.

In 1625 he had to surrender Breda to the Spanish general Ambrogio Spinola after a siege of 11 months.

On 4 December 1597 he married Anne, Baronesse de Mérode (9 January 1567 – Leiden, 8 October 1634) and had three children.