It looks possible that eh was illegitimate, from this accunt by John Brandon:

From: starbuck95@hotmail.com (John Brandon)
Newsgroups: soc.genealogy.medieval
Subject: Ralph Stafford + Matilda/Maud Hastang
Date: 10 Jun 2004 06:04:47 -0700

Back in 2000, Peter Sutton wrote that Sir John de Stafford of
Bramshill and his wife Margaret (nee Stafford) had "three children,
Sir Humphrey Stafford, Ralph Stafford of Grafton and Joan.  Ralph
Stafford of Grafton married Maud Hastang, daughter and coheiress of
another Sir John de Hastang of Chebsey ..."

There's no indication in this that the son Ralph Stafford of Grafton
was illegitimate.  But on the A2A catalogue, we find ...

   FILE  [no title] - ref.  3764/169  - date: 1373
      [from Scope and Content] Notarial instrument of William de
Nauhagh clerk, regarding the marriage of Ralph de Stafford
illegitimate son of Lady Margaret de Stafford to Matila daughter of
John Hastang deceased in the church of St. Bertelin.

(from the Phillipps Collection [documents relating to Staffordshire
from the collections of Sir Thomas Phillipps--Catalogue Ref. 3764]).
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