William de la Plaunche - Who is William de la Plaunche?

Regarding William de la Planche
First, there is a discussion on Wikitree that provides some insight based on a supposed coat of arms (without comment on the reference to “cousin of Queen Eleanor of Castile”)

“...There exists in France today a family using the surname "de Fiennes de la Planche," whose arms are those of the Fiennes, though with slight differencing in tincture and charge that suggests either cadency or bastardy: a lion rampant on a field billetty, with (in different versions) a bend or a baton for difference. The Fiennes arms lack the billets and the bend or baton.

The 13th century William de la Plaunche who was Eleanor of Castile's kinsman also bore the lion rampant on a field billetty, as did his issue in England through his son James de la Planche, who in 1289, by Queen Eleanor's agency, married Maud de Haversham, an heiress in Buckinghamshire. In addition to Alice and James, William de la Planche also had a son John, who received gifts from Edward I and Queen Eleanor when they arrived in France in the spring of 1286.

The dates of William de la Planche's children's marriages suggests that like Queen Eleanor, he was a great-grandchild of Count Aubri II of Dammartin and a grandson of Aubri's daughter Agnes, who married William de Fiennes I. It seems very likely that the de Fiennes de la Planches originated with a younger son of William de Fiennes I and Agnes de Dammartin.”

My primary source for issues of heraldry identifies two cadet branches of the House of Fiennes
1. House of de la Planche, Lords of Wendover, Cheriton and Haversham
Issued from Guillaume, younger son of Guillaume I de Fiennes
English branch, and
2. House of Fiennes-Heuchin, Lords of Heuchin, La Porte and La Planche
Issued from Robert, younger son of Enguerrand II de Fiennes
The house of Planche could be described as argent, a lion rampant sable crowned d’Or, gouge (gutty) which means a seme of droplets. The house of Fiennes-Heuchin could be described as argent, a lion rampant armed and langued gules, bilette (billety) which means a seme of billets (small rectangular shapes)
As can be seen, one branch (probably English) were lords of Wendover, Cheriton and Haversham, while the other (probably French) were lords of Heuchin, La Porte and La Planche.

Also, the senior branch of House of Fiennes we’re Lords of Tingry, Ruminghem and Wendover, Barons of Fiennes and Castellans of Bourbourg indicating that the heraldry used by the senior line, argent a lion rampant sable, was used in both England and France. The distinction will take place between the male born in France who settled in England then his son born in England who would become the progenitor of the English branch.

Second, following a discussion by George F. Farnham F. S. A., (https://www.le.ac.uk/lahs/downloads/ClaybrookePagesfromXIIpartII-5.pdf ) of whom it is said with regards to “The Victoria County History of Leicestershire”, “sound scholarship, critical insight, an accurate sense of selection, and a fidelity to the original texts which allows them to lose nothing of their force and precision in translations and summaries, are the rare but necessary gifts that have enabled Mr. Farnham's untiring patience to produce this result... the work which Mr. Farnham has done for Leicestershire in these four volumes is more complete in shape than any work of the kind that has been done for other counties...”, in which he lays out the descent of the manor of Claybrooke which, with the marriage of Matilda Haversham as her 1st husband to James de la Planche who at his death in 1306 was seized of the manor of Claybrooke in right of his wife (jure uxoris)... the attached genealogical tables showing the descendency from James through several Williams’s.

Then thirdly, I was lucky this morning and bypassed the Stirnet pay wall. Stirnet shows a possible solution supported by an interpretation of Lipscomb and Collins.

(1) *Enguerand de Fiennes (c. 1128 - 1189) = Sibille de Tingry

  A. William de Fiennes of Wendover (1160 - 1240) = Agnes Dammartin

     A.1. William II de Fiennes of Wendover (c. 1240- 07/11/1302 at the battle of Courtrai) = Blanche de Brienne (note that Wikipedia indicates that Blanch married twice, 1st to William II de Fiennes and 2nd to William de la Planche!?)

     A.2 Giles de Fiennes (c. 1250 - 1293) = Sybilla de Fillol

. .
. .
(2) Baldwin
(3) William (Guillaume)de Fiennes aka William de la Plaunche <<<!

  B.1 William de la Plaunche

     B.1.1 James de la Plaunche of Haversham (d. 1306) = Maud (Matilda) de Haversham.

Beyond this the pedigree is supported by Lipscomb (Bucks, vol 4, pedigree of Haversham, p. 187) which is also shown in the article referenced above by Farnham.

So we have (Sir) James de la Plaunche son of William de la Plaunche son of William de Fiennes aka William de la Plaunche brother of Enguerand and Baldwin sons of Conan son of Eustache who reportedly fought at Hastings in 1066, kin of William the Conqueror. The ascendancy of Eustache is well established in Geni. We have the ascendancy above and the descendency below tied to this middle 3 generations, however...

• Lipscomb shows Enguerand as son of John son of James son of Alan “descendt of John”, all of whom were shown as Hereditary constables of Dover Castle, and Collins confirms that he was descended from said constables. I note that Carl Gustav Verbraeken recently updated the profile for Eustache de Fiennes to indicate an aka of Alan so this should tie that person down, but there appears to be an unconventional use of English and French given names that is confusing things, we may have the same person(s) owning land and title in both England and France with given names being confounded.

I’ve added the two coats of arms in question to the media tab