Manuel, Hereditary Prince of Portugal
Manuel of Portugal( c. 1568–22 June 1638) was the illegitimate son of António, Prior of Crato, pretender to the Portuguese throne during the 1580 Portuguese succession crisis.
He secretly married in 1597 Countess Emilia of Nassau, daughter of William the Silent and Anna of Saxony.
Otto I, Count of Nassau
Otto I of Nassau,( † between 3 May 1289 and 19 March 1290) was Count of Nassau and is the ancestor of the Ottonian branch of the House of Nassau.
Elisabeth of Nassau-Dillenburg, Countess of Wied
Elisabeth of Nassau-Dillenburg (1 December 1488 – 3 June 1559 in Dillenburg) was a member of the House of Nassau.
She was a daughter of John V of Nassau-Dillenburg and his wife Elisabeth of Hesse-Marburg.
Her brothers were Henry III of Nassau-Breda, John of Nassau-Vianden-Dietz, Ernest of Nassau and William the Rich.
Her sister was Maria of Nassau.
Maria Belgica of Portugal
Maria Belgica of Portugal, also known as Maria Belgica of Crato( born before 12 October 1598 – 28 July 1647), was the daughter of Manuel of Portugal, son of the self- proclaimed Portuguese king António of Crato, and Countess Emilia of Nassau( 1569 – 1629), the youngest daughter of William of Orange.
Countess Emilia Antwerpiana of Nassau
Countess Emilia Antwerpiana of Nassau( Antwerp, 9 December
1581- Landsberg, 28 September 1657) was the sixth and youngest daughter of William the Silent and his third wife, Charlotte of Bourbon.
Frederick Augustus, Duke of Nassau
Friedrich August, Duke of Nassau, Prince of Nassau- Usingen( 23 April 1738 in Usingen – 24 March 1816 in Wiesbaden) was the last Prince of Nassau- Usingen and, jointly with his cousin, Friedrich Wilhelm of Nassau- Weilburg, first Duke of Nassau.
He died without surviving male issue and was succeeded by his cousin's son, Wilhelm.
Countess Emilia of Nassau
Countess Emilia of Nassau (10 April 1569 – 16 March 1629) was the third and youngest daughter of William the Silent and his second wife Anna of Saxony.
Henry I, Count of Nassau-Siegen
Henry I of Nassau- Siegen,( – between 13 July and 14 August 1343) was Count of Nassau- Siegen, a part of the County of Nassau, and ancestor of the House of Nassau- Siegen.
He comes from the Ottonian branch of the House of Nassau.
Anna of Saxony
Anna of Saxony (23 December 1544 – 18 December 1577) was the heiress of Maurice, Elector of Saxony, and Agnes, eldest daughter of Philip I, Landgrave of Hesse.
Maurice's only son, Albert, died in infancy.
Anna was the second wife of William the Silent.
Anna was born and died in Dresden.
Her wealth drew many suitors; before the proposal of Orange in 1560, there were negotiations with the Swedish royal house.
She accepted the suit of William I of Orange, and they were married on 25 August 1561.
Walram II, Count of Nassau
Walram II of Nassau,( – 24 January 1276), was Count of Nassau and is the ancestor of the Walramian branch of the House of Nassau.

Question: When did Countess Emilia Of Nassau's mother die?
Answer: 18 December 1577