6. The House of Lancaster was descended from Edward III and Princess Philippa d'Oisy of Hainault and Holland. Together, they had many sons. Which one founded the Lancastrian Line?
From Quiz The Royal House of Lancaster
Answer: Duke John of Gaunt Plantagenet of Lancaster
Duke John de Gaunt Plantagenet of Lancaster was born in March 1340 in St Bavon's Abbey, Ghent, Flanders, France. He was married three times. Firstly on 19 May 1359 in Reading Abbey, Berkshire, England to Countess Blanche Plantagenet of Lancaster, the daughter of Duke Henry Grosment Plantagenet of Lancaster and Isabella de Beaumont. Secondly on 21 Sep 1371 in Roquefort, Guienne to Infanta Princess Constance Trastamara of Castile and Leon, the daughter of King Pedro I the Cruel Trastamara of Castile and Leon and Marie de Padilla. And thirdly, on 13 Jan 1396 in Lincolnshire, England to Catherine Swynford Roet.
Throughout his life, he was a regent for his nephew the child king and even pressed a claim as the King of Castile through his second wife, when her father died without a male heir. John of Gaunt died on 3 Feb 1399 in Lincolnshire, England.