Thomas Chaucer was a relative by marriage of John of Gaunt, 1st Duke of Lancaster, through his aunt Katherine Swynford.
Katherine (born Roet) was the sister of his mother, Philippa Roet.
Swynford was first Gaunt's mistress, and then his third wife.
 Their four children,  John Beaufort, Henry Beaufort, Thomas Beaufort and Joan Beaufort, were first cousins to Thomas Chaucer, and all prospered: John's family became Earls and subsequently Dukes of Somerset, Henry a Cardinal, Thomas became Duke of Exeter, Joan became Countess of Westmorland and was grandmother of Kings Edward IV and Richard III.
 
King Henry IV - son of John of Gaunt by his first marriage to Blanche of Lancaster - was half-brother to Thomas Chaucer's Beaufort first cousins.
Thomas was able to buy Donnington Castle for his only daughter Alice.
Thomas Chaucer was a relative by marriage of John of Gaunt, 1st Duke of Lancaster, through his aunt Katherine Swynford. Katherine (born Roet) was the sister of his mother, Philippa Roet. Swynford was first Gaunt's mistress, and then his third wife.  Their four children,  John Beaufort, Henry Beaufort, Thomas Beaufort and Joan Beaufort, were first cousins to Thomas Chaucer, and all prospered: John's family became Earls and subsequently Dukes of Somerset, Henry a Cardinal, Thomas became Duke of Exeter, Joan became Countess of Westmorland and was grandmother of Kings Edward IV and Richard III.  
King Henry IV - son of John of Gaunt by his first marriage to Blanche of Lancaster - was half-brother to Thomas Chaucer's Beaufort first cousins. Thomas was able to buy Donnington Castle for his only daughter Alice.
Thomas Chaucer