While in Pavia recently, I had the pleasure of meeting the geneticists Enza Battaglia, Anna Olivieri and Antonio Torroni, who are an important part of the Auramala Project. The Project is investigating the Fieschi Letter, which was addressed to Edward III and informed him how his father Edward II had escaped from Berkeley Castle in 1327 and ended up in Italy. They're also searching through Italian archives to find possible documentation supporting Edward II's survival in Italy in the 1330s, and ultimately attempting to find descendants who share Edward's mitochondrial DNA, in case the possibility arises some day to test Edward's remains (see here for their posts about this). I'm helping with the genealogy part, and have found a line from one of Edward's sisters in the female line down to the 1700s (so far).
I've also looked at Edward's maternal ancestry, his mother Eleanor of Castile, grandmother Joan of Ponthieu, great-grandmother Marie of Ponthieu, great-great-grandmother Alais of France, and so on. I got the maternal line back to the mid-900s to Edward's ten greats grandmother. Unfortunately, tracing the female descendants of Edward's female ancestors hasn't proved fruitful yet and I haven't been able to find any lines of descent past the fifteenth century, though it has thrown up some interesting people with whom Edward shared mitochondrial DNA: Henry the Young King's wife Marguerite of France (Edward's great-great-great-aunt; her husband was Edward's great-great-uncle); Richard Lionheart's queen Berengaria of Navarre (granddaughter of Edward's great-great-great-grandmother Berenguela of Barcelona) and her nephew Thibault the 'Troubadour King' of Navarre; Jeanne de Penthièvre, duchess of Brittany in her own right (c. 1319-1384), great-great-granddaughter of Agatha of Ponthieu, younger sister of Edward's grandmother Joan of Ponthieu, queen of Castile; Constance of Béarn, viscountess of Marsan (d. 1310), who married Edward I's first cousin Henry of Almain, and who was, like Edward II, descended in the female line from Gerberga of Provence, countess of Provence and Arles (d. 1115).
Edward II had numerous sisters, but only five lived into adulthood: Eleanor, Joan of Acre, Margaret, Mary and Elizabeth. Mary became a nun, so is out. Margaret had only one son, Duke John III of Brabant, so is out. Eleanor had one daughter, Joan of Bar, countess of Surrey, who had no children, so is out. That leaves Joan of Acre, countess of Gloucester and Hertford (1272-1307) and Elizabeth, countess of Holland, Hereford and Essex (1282-1316). Elizabeth had two daughters: Eleanor le Boteler or Butler née de Bohun, countess of Ormond (c. 1310-1363) and Margaret Courtenay née de Bohun, countess of Devon (1311-1391, the last survivor of Eleanor of Castile's grandchildren), both of whom had daughters. Joan of Acre had five daughters: Eleanor de Clare who married Hugh Despenser the Younger and William la Zouche; Margaret de Clare who married Piers Gaveston and Hugh Audley; Elizabeth de Clare who married John de Burgh, Theobald de Verdon and Roger Damory; Mary de Monthermer who married Duncan MacDuff, earl of Fife; and Joan de Monthermer, who became a nun. I can't find any female descendants for Eleanor de Clare; although she had five daughters (Isabella, Joan, Eleanor, Margaret and Elizabeth Despenser), none of them had any daughters of their own. Isabella Despenser had one son, Edmund Fitzalan, and Elizabeth Despenser four sons including Thomas, Lord Berkeley. The other three Despenser daughters were forcibly veiled as nuns by Edward II's queen Isabella of France a few weeks after she had their father executed on 24 November 1326, even though they were only children at the time. Mary de Monthermer had one daughter Isabella MacDuff, who had one daughter Elizabeth Ramsay, who died childless. So of Joan of Acre's five daughters, that leaves two, Margaret and Elizabeth de Clare, who had daughters, granddaughters, great-granddaughters and so on, as well as their cousins Eleanor and Margaret de Bohun, the two daughters of Joan of Acre's sister Elizabeth. Thus, there are four nieces of Edward II who are relevant to this research.
I still need to do more research into the female descendants of Eleanor de Bohun, who had two daughters, Margaret de Bohun, who had seven or eight daughters, and their cousin Margaret de Clare's daughter Margaret Audley, who had four daughters. (Margaret de Clare's other daughter Joan Gaveston died young in 1325.) Elizabeth de Clare, Joan of Acre's third daughter, had two daughters: Isabella de Verdon (21 March 1317 - 25 July 1349) and Elizabeth Damory (shortly before 23 May 1318 - c. 1361/62). Elizabeth Damory herself had two daughters, Agnes and Isabel Bardolf, who are named in their grandmother Elizabeth de Clare's 1355 will when she left them bequests in aid of their marriages, but they disappear from history after that. If they did marry and have children, there's no record of it, and it seems likely that they either died before they could marry or that they became nuns. So that's the end of that line, unfortunately (the line of Elizabeth Damory's son William Bardolf continued, but that's irrelevant for our purposes).
Isabella de Verdon, Edward II's great-niece, to my joy, turned out to be a key figure. Here's the story of how she came to be born. Elizabeth de Clare (16 September 1295 - 4 November 1360) was widowed from her first husband, the earl of Ulster's son and heir John de Burgh, on 18 June 1313. She was not yet eighteen years old and had a baby son William Donn ('the Brown') de Burgh, later earl of Ulster, born on 17 September 1312 (William's daughter and heir Elizabeth de Burgh, born in 1332 and named after his mother, married Edward III's second son Lionel of Antwerp). Elizabeth de Clare remained in Ireland for some time after John de Burgh's death. On 24 June 1314, her elder brother Gilbert de Clare, earl of Gloucester, was killed at the battle of Bannockburn, leaving Elizabeth and their other sisters Eleanor and Margaret as his heirs. In late 1315, Elizabeth's uncle Edward II ordered her back from Ireland, where she had (I imagine) been living under the protection of her father-in-law Richard de Burgh, earl of Ulster. Edward presumably wished to marry Elizabeth off to a man of his choosing, as he did later when he more or less forced her to marry his current court favourite Sir Roger Damory.
Unfortunately for Edward II but more especially for Elizabeth, Theobald de Verdon had other ideas. Theobald was the justiciar of Ireland, seventeen years older than Elizabeth (born on 8 September 1278), and the widower of Roger Mortimer of Wigmore's sister Maud, with whom he had daughters Joan, Margery and Elizabeth de Verdon. On 4 February 1316, Theobald abducted the twenty-year-old Elizabeth de Clare from Bristol Castle where she was then staying, and married her. As Elizabeth was an adult, a widow and a mother, this may not have been as traumatic as the later abduction of her teenaged niece Margaret Audley must have been, but still. Theobald claimed to Elizabeth's enraged uncle Edward II shortly afterwards when he visited the Lincoln parliament that Elizabeth had come to him willingly, but then he would say that, wouldn't he?
After less than six months of married life with his probably reluctant bride, Theobald de Verdon died on 27 July 1316, only in his late thirties. Elizabeth's feelings on the matter are unknown, but fortunately for us, Theobald left her about a month pregnant at the time of his death. Sometime during her pregnancy, Elizabeth retired to Amesbury Priory in Wiltshire, where her aunt Mary, Edward II's sister, was a nun (the two women evidently were extremely fond of each other). At Amesbury on 21 March 1317, eight months after the death of Theobald, Elizabeth gave birth to their daughter Isabella de Verdon. Edward II, staying at the nearby royal palace of Clarendon, sent a silver cup with stand and cover as a christening gift for his latest great-niece, having received news of the birth from a messenger sent by his sister Mary. Queen Isabella was chosen as godmother and travelled from Clarendon to Amesbury to attend the christening; the baby was named after her. Roger Martival, bishop of Salisbury, performed the ceremony. Isabella de Verdon was one of the four co-heiresses of her father, with her three older half-sisters (nieces of Roger Mortimer); primogeniture did not apply to women, and daughters inherited equally. Elizabeth de Clare was still recovering from the birth when Edward II came to Amesbury and put pressure on her to marry his current 'favourite', Roger Damory. Elizabeth, who really had no choice, married Damory a few weeks later, and their only child Elizabeth Damory was born shortly before 23 May 1318, only fourteen months after her half-sister Isabella de Verdon.
Sometime in the late 1320s when she was still only a child, Isabella was married to Henry, Lord Ferrers of Groby in Leicestershire, who was much her senior. born by 1304 at the latest and perhaps in the 1290s. Henry, unfortunately, claimed his conjugal rights early: Isabella gave birth to her eldest child probably in February 1331 (her mother sent her gifts for her purification ceremony that March, around the time of her fourteenth birthday). The child, not surprisingly, did not survive. Luckily. this early experience of childbirth did not damage Isabella's body, and she gave birth to four more children, two sons and two daughters including Elizabeth Ferrers, who was born probably sometime in the mid or late 1330s. Elizabeth Ferrers married David de Strathbogie, titular earl of Atholl, who was born in the early 1330s as the son of David de Strathbogie the elder and Katherine Beaumont, one of the daughters of Henry, Lord Beaumont. Katherine's sister Isabella Beaumont married Henry of Grosmont, first duke of Lancaster, and David the younger was thus the first cousin of Blanche of Lancaster, who married Edward III's third son John of Gaunt, and his paternal grandmother was Joan Comyn (actually both of his grandmothers were Comyns). Elizabeth Ferrers and David de Strathbogie had a daughter Elizabeth de Strathbogie, who had a daughter Elizabeth Scrope, who had a daughter Elizabeth Clarell, and so on down the centuries until the 1700s at least. More work is still to be done, tracing this line further.
If you've done any genealogical research and are aware of any female lines from Edward II's sisters or their maternal ancestors, please contact either me or the Auramala Project!