Many sources on World Connect have William as son of Robert le Strange & Eleanor de Blancminster. However the post to soc.genealogy.medieval by Chris Phillips, shown below, indicates a different ancestry:
From: Chris Phillips (cgp@@medievalgenealogy.org.uk)
Subject: Early Feltons (was: The Grey sisters of Heton)
Newsgroups: soc.genealogy.medieval
Date: 2002-06-23 02:17:41 PST
> The vol.12 pedigree also shows a father for Robert and William:
> "Robert (of Felton), to whom his father granted in 1260/1 half the manor of
> Litcham, saving the manor house" [citing Eyton, Shropshire, vol.x, p.274].
> Robert has a sister "Alice, to whom her father granted half the manor of
> Litcham and the advowson."
> The father of Robert and Alice is shown as "John L'Estrange of Litcham,
> Norfolk" [citing the Hunter Blair article, p.76].
A bit more searching shows that this suggestion, that the father of William and Robert de Felton was Robert, son of John Lestrange, is actually rather a bizarre one.
The text accompanying the "revision" of the pedigree in the History of Northumberland turns out to be lifted, more or less word-for-word, from the article by Hunter Blair in Archaeologia Aeliana, 3rd series, vol.20. The basis of the claim is:
(1) that on heraldic evidence the Feltons of Northumberland were closely connected, "either by blood or by marriage" with the Stranges of Knockin, and that "therefore they took their name from Felton (now West Felton) near that place".
(2) John L'Estrange about 1260/1 gave his daughter Alice half his manor of Litcham, Norfolk, with the advowson of the church, and the other half to his son Robert [citing Eyton, vol.10, p.274, a reference I haven't seen]. Hunter Blair continues "It seems to me either that Robert was surnamed of Felton , which appears the more probable, or else that Alice had married a Felton, of which I can find no proof."
What makes this bizarre is that, as far as I can see, the John L'Estrange who made a grant to his son Robert and daughter Alice about 1260/1 -if that date's correct - must have been John Lestrange III of Knockin (d. bef. 26 March 1269)* [Complete Peerage, vol.12, pt 1, pp.350,351]. [*John Lestrange II was already dead, and the son and heir of John Lestrange IV was not born until around 1254]
John Lestrange III did have a son Robert (d. on or before 12 October 1276) [CP vol.12, pt 1, p.341], but this Robert is well documented as the ancestor of the Lords Strange of Blackmere. He was succeeded first by his son John (d. 1289), then by another son Fulk (b. c.1267). I can't see any indication that Robert called himself "Robert de Felton", or that he had sons called Robert or William.
Instead, the Complete Peerage explains the Strange connection by saying that Robert, the presumed elder brother of William de Felton, married Hawise (elsewhere called Maud), a daughter of John Lestrange IV [CP vol.5, p.290]. The later inquisition post mortem of Thomas de Felton (1381) is abstracted by CP as "the only authority for the pedigree", and says that John Lestrange gave the manor of Litcham to Robert de Felton and Maud his wife, and their heirs male (with reversion to the Stranges), and that Roger Lestrange in 1381 was s and h of Roger, s and h of John, s and h of John, s and h of the John who made the gift - that sequence implies the gift was made by John IV.
The CP scheme looks reasonable enough, although from the CP account it looks as though there's nothing in the sources to specify Hawise's relationship to the John Lestrange who made the grant. It is a bit odd that Robert's wife is called Hawise in the contemporary records but Maud in Thomas's inquisition post mortem. The other point is that It would leave the Feltons of Edlingham without a descent from the Stranges, so the similarity of the Felton and Strange coats of arms would have to be explained by the Feltons being tenants, rather than descendants of the Stranges.
Apart from that, the only clue to the Feltons' ancestry I've seen is provided by Blomefield (Norfolk, vol.10, p.10), who says that the Robert who held Litcham in the 1290s was presumably the same man who was knighted with the Prince of Wales about the same time, who was described as "Robert, son of Robert, son of Pagan". This seems to be connected with the extracts from the Dictionary of National Biography, quoted by Ian Fettes, according to which the common ancestor was "Pagan of Upper Felton, Northumberland" (though the Strange link indicates West Felton in Shropshire as the place of origin). However, if I've understood correctly, according to the DNB, Robert and William (usually assumed to be brothers) were first cousins, the sons of William and Robert respectively, who were the sons of Pagan. Obviously more information is required to sort this out.
Chris Phillips