Daughter of a knight from Hainaut, Katherine, whose name is also spelled 'Katharine' or 'Catherine',[2] was brought up at the English royal court, later found herself in the service of Blanche of Lancaster, the first wife of John of Gaunt.

[4] In the early 1390s, the love affair between Katherine and John of Gaunt resumed, and after the death of his second wife, the Duke unexpectedly married his mistress in 1396, which caused discontent among the English nobility.

Katherine's father was Paon de Roet, a herald and, later, knight (who was "probably christened as Gilles"[1]), who came to England in the entourage of Philippa of Hainaut, who married King Edward III.

On this basis, it has been suggested that he was related to the powerful family of the Lords of Le Roeulx, who owned a lordship in the County of Hainaut, whose name was spelled differently: Rouet, Roëlt, Ruet.

In 1631, John Weever claimed that she was the eldest of Paon de Roet's daughters, but that would make her at least 28 years old at the time of her first marriage, which is much older than the typical age girls married.

Jean Froissart reports that Katherine's tutor in her youth was Blanche of Lancaster, a close relative of the King and the bride of his third surviving son, John of Gaunt.

The origin of Blanche was recorded in 1396 by John of Gaunt, who, submitting a petition to the Pope for permission to marry Katherine, indicated that he was the godfather of her daughter, “born from another man”,[e] adding that he did not advertise this fact.

The girl was probably named after the Duke's wife; she later enjoyed the patronage of Gaunt: in 1375 he granted Katherine custody of the heir Sir Robert Deincourt, who was betrothed to Blanche.

In addition, Weir points out that in the church at Irnham on the tombs and stained glass windows there are coats of arms of several prominent Lincolnshire families related by marriage, including Swynford and Thymelby.

[15][16] Shortly before 21 January 1365, John Bokyngham, Bishop of Lincoln, conferred on Katherine the privilege of privately church worship whenever she visited Leicester, which, according to Alison Weir, indicates that she was not only devout, but also a quite important and respected parishioner.

[20] In August–September 1369, Hugh Swynford, as part of the army of John of Gaunt, participated in a military campaign in France, where the Hundred Years' War resumed; he returned to England probably in November.

This included clothing for Blanche Swynford, "damuselle of the daughters of the Duke of Lancaster", which, according to Weir, indicates that the Queen showed concern for Katherine and her family until the end of her life.

In the spring of 1372 John of Gaunt and the King helped her financially; and in the summer of the same year, Katherine was present at the birth of the first child by Duchess Constance, a daughter called Catherine.

Jean Froissart wrote that the love affair began during the lifetime of Blanche of Lancaster and Hugh Swynford, but he sometimes made mistakes in his chronicle (in particular, he pointed out that Katherine gave birth to three children from John of Gaunt, although there were four of them).

Also, some later studies indicate that the love affair between Katherine and John of Gaunt began during the life of her first husband, and her eldest son Thomas Swynford was "a child from two fathers", but this seems unlikely to modern researchers.

In the document of the grant of an annuity to Katherine Swynford by King Richard II dated 7 June 1392, it is indicated that her first-born son with the Duke of Lancaster, John Beaufort, was 21 years old.

[6][24][25] Due to Hugh Swynford's heir, Thomas, being a minor at the time of his father's death, the family estates usually passed into the custody of the overlord, in this case the King and Duke of Lancaster.

Henry Knighton, writing his chronicle after 1378, indicates that Katherine served in the household of Duchess Constance, but none of the Duke's grants made to his mistress during this period state that they were given for service to his wife.

[30] On 12 September 1374, Katherine may have been present, along with John of Gaunt, who had returned from France, at a memorial ceremony in honor of the late Duchess Blanche, held at St. Paul's Cathedral, although there is no documentary evidence of this.

Also, according to the order of the Duke, which may date back to 1375 or 1377, Katherine was presented with tenement houses on the east bank of the River Witham in the Lincolnshire port of Boston, formerly owned by Geoffrey de Sutton.

Although it has been hypothesized that the future Cardinal was the youngest of Katherine's sons, since in 1398 he was called a "boy" when he was appointed Bishop of Lincoln, but, according to Alison Weir, this epithet was simply a derisive comment on Henry's elevation to the bishopric at the age of 23.

It is possible that Katherine, who was the governess of the late monarch's granddaughters, was in London during this period, but it is unlikely that she often saw the Duke busy preparing for the coronation of his infant nephew and new King Richard II.

[6][45] On 20 October 1383 King Richard II, who apparently sympathized with Katherine, granted her the right to fence 300 acres of land and forest on the estate of Kettlethorpe,[46] and in April 1387, he made her a Lady of the Order of the Garter, which during this period was considered the highest honor an Englishwoman could receive.

The eldest son, John Beaufort, who "was a great favorite of his father", in the spring of 1390 took part in a large jousting tournament at Saint-Inglevert near Calais, after which he began to participate in military campaigns.

In addition, his heir, Henry Bolingbroke, was on bad terms with King Richard II, and in September 1398 he was expelled from England by royal order, which, by all accounts, aggravated the Duke's illness.

Three years before her death (28 November 1437) Joan received permission from King Henry VI to establish a chapel with two chaplains to serve daily at the altar in front of her mother's grave.

[68] The frontispiece to an early 15th-century manuscript of the epic poem Troilus and Criseyde by Geoffrey Chaucer depicts the poet reading it to the royal court of King Richard II.

[68] The respect that Katherine enjoyed in the royal family probably indicates that she was quite skilled in court duties, had exquisite taste, was sociable, polite, literate, intelligent and, most likely, was a good conversationalist.

After Richard III became king in 1483, he publicly declared that Henry had no right to the throne, since the Beauforts were descended from "double adultery" (from the connection of John of Gaunt and Katherine Swynford), which was accepted by many as a fact.

However, as Alison Weir (on which the novel had a huge impact[71]) notes, this work is primarily a novel about the ideal romantic heroine – beautiful, sensual and loving, and Seton gave Katherine many moral, emotional, and psychological qualities and cultural aspects from her own life.