Blanche fitzJohn

The illegitimate daughter of John of Gaunt by Marie de St. Hilaire of Hainaut, mistress:

Blanche (1359–1388/89), illegitimate, married Sir Thomas Morieux (1355–1387) in 1381, without issue. Blanche was the daughter of John's mistress, Marie de St. Hilaire of Hainaut (1340 – after 1399), who was a lady-in-waiting to his mother, Queen Philippa. The affair apparently took place before John's first marriage to Blanche of Lancaster. John's daughter, Blanche, married Sir Thomas Morieux in 1381. Morieux held several important posts, including Constable of the Tower the year he was married, and Master of Horse to King Richard II two years later. He died in 1387 after six years of marriage. [https://en.wikipedia.org/wiki/John_of_Gaunt#Children]