Before 01 Oct 1369 [his father] Robert Willoughby 4th Baron Willoughby (age 20) and [his mother] Margery Zouche Baroness Willoughby Eresby (age 30) were married.

In or before 1380 [his future brother-in-law] John Strange 6th Baron Strange Knockin (age 29) and Jane Charleton Baroness Strange Knockin (age 23) were married. She by marriage Baroness Strange Knockin. They were fourth cousins. She a great x 3 granddaughter of King Edward "Longshanks" I of England.

In or before 1381 1369 [his future brother-in-law] John Strange 6th Baron Strange Knockin (age 18) and Maud Mohun Baroness Strange Knockin (age 23) were married. She by marriage Baroness Strange Knockin. They were fourth cousins.

After 03 Jan 1383 William Willoughby 5th Baron Willoughby (age 13) and Lucy Strange Baroness Willoughby Eresby were married. They were third cousins.

Before 1387 [his son-in-law] Henry Beaumont 5th Baron Beaumont (age 7) and [his daughter] Elizabeth Willoughby Baroness Beaumont (age 2) were married. She by marriage Baroness Beaumont. They were third cousin once removed. He a great x 4 grandson of King Henry III of England.

After 17 Oct 1388 [his father] Robert Willoughby 4th Baron Willoughby (age 39) and [his step-mother] Elizabeth Latimer 5th Baroness Latimer, Baroness Neville and Willoughby (age 31) were married. She by marriage Baroness Willoughby de Eresby.

On 04 Nov 1393 Edmund of Langley 1st Duke York (age 52) and [his future wife] Joan Holland Duchess York (age 13) were married. She by marriage Duchess York. The difference in their ages was 38 years. She the daughter of Thomas Holland 2nd Earl Kent (age 43) and Alice Fitzalan Countess Kent (age 43). He the son of King Edward III of England and Philippa of Hainault Queen Consort England. They were half second cousin once removed. She a great x 2 granddaughter of King Edward "Longshanks" I of England.

Before 09 Aug 1404 William Willoughby 5th Baron Willoughby (age 34) and Joan Holland Duchess York (age 24) were married. She by marriage Baroness Willoughby de Eresby. She the daughter of Thomas Holland 2nd Earl Kent and Alice Fitzalan Countess Kent (age 54). She a great x 2 granddaughter of King Edward "Longshanks" I of England.

Before 18 Nov 1406 [his son-in-law] William Fitzhugh 4th Baron Fitzhugh (age 7) and [his daughter] Margery Willoughby Baroness Fitzhugh (age 9) were married. He the son of Henry Fitzhugh 3rd Baron Fitzhugh (age 48) and Elizabeth Grey Baroness Fitzhugh (age 42).

Before 1407 Thomas Montagu 1st Count Perche 4th Earl Salisbury (age 18) and [his sister-in-law] Eleanor Holland (age 20) were married. She the daughter of Thomas Holland 2nd Earl Kent and Alice Fitzalan Countess Kent (age 56). He the son of John Montagu 3rd Earl Salisbury and Maud Francis Countess of Salisbury (age 42). They were half third cousin once removed. He a great x 3 grandson of King Edward "Longshanks" I of England. She a great x 2 granddaughter of King Edward "Longshanks" I of England.

After 06 Sep 1410 Henry Scrope 3rd Baron Scrope Masham (age 37) and [his former wife] Joan Holland Duchess York (age 30) were married. She by marriage Baroness Scrope Masham. She the daughter of Thomas Holland 2nd Earl Kent and Alice Fitzalan Countess Kent (age 60). She a great x 2 granddaughter of King Edward "Longshanks" I of England.

Before 27 Apr 1416 Henry Bromflete 1st Baron Vesci (age 9) and [his former wife] Joan Holland Duchess York (age 36) were married. There appears to be a twenty-seven year age gap here which may suggest the marriage ewas a reward to him since she, having being married three times before, including to Edmund of Langley 1st Duke York, would be a wealthy widow. The difference in their ages was 26 years; she, unusually, being older than him. She the daughter of Thomas Holland 2nd Earl Kent and Alice Fitzalan Countess Kent (deceased). She a great x 2 granddaughter of King Edward "Longshanks" I of England.

[his son] Thomas Willoughby of Parham and Joan Fitzalan were married. The difference in their ages was 20 years. They were second cousin once removed. She a great x 4 granddaughter of King Henry III of England.