Some genealogies show a Joan D'Oyley, born 1313 in Gretworth, Northamptonshire with other data similar to this Joan, including marriage to Thomas Lewknor, born in 1344. No documentation has been found for such a person.
Husband: Thomas de Lewknor, Knight, son of Roger de Lewknor, Knight,  by Katherine Bardolf, daughter of and heiress of (Unknown) Bardolf. 
Wife: Joan D'Oyley, daughter of John d'Oyley, Knight,  by Margaret, daughter of Thomas de Tregoz, Knight, 2nd Lord Tregoz
Date: (as his 2nd wife by settlement dated) 1370 
Estate: Blymhill Manor
"Sir John D'Oyly, Knt., succeeded to his mother's estates at Raunton and elsewhere, and dying about 7 Edw, II., left issue by his first wife, Joane, daughter of Sir Robert de Knightley, of Knightley, Knight, an elder son of Sir John D'Oyly, Knight, who was of Stoke, near Oundle, co. Northampton, in right of his wife Alice, daughter and heiress of John de Stoke, to whom he was married before December, 1299. He died about 1319, not long after his father, but at 50 years of age. He was succeeded at Raunton and Stoke D'Oyly by his eldest son, Sir Thomas D'Oyly, Knight, who had married, before the year 1313, Margaret, a near connection (and probably sister of Humphry Hastang, of Nassington, co. Northampton, by whom he had an elder son John. Sir Thomas died about 1336, and was probably slain in the Scotch wars in which he which he was serving, His son Sir John D'Oyly, Knight, succeeded to Raunton, and had issue by his wife Margaret, daughter and in her issue the heiress of Sir Thomas Tregoze, Knight of Goring, in Sussex, a son Sir Thomas D'Oyly, Knight, who succeeded his father about 1363 but died without issue in or before 1370, and a daughter Joane, who became sole heiress to her brother. Joane D'Oyly was twice married, first about 1363 to Sir Thomas Lewknor, Knight, Lord of Gretworth, co. Northampton, Bradhurst in Sussex, and South Mymmes, co. Middlesex, who died in 1375, set. 27, and by whom she had an elder son Roger Lewknor. The heiress of D'Oyly married secondly, in 1376, John Deiing, alias de Cobeham, of co. Kent, by whom she had no surviving issue, and died about 1394. In 1391 she and her husband John de Cobeham demised the manor of Raunton to her kinsman John de Knightley for term of his life, to be held by the yearly render of a rose ; with remainder to her issue by John de Cobeham, with remainder to her own right heirs."
Sir Thomas Lewknor, Esq., married Elizabeth Carew. M.P. 1404; Died 1471.  * Also called Roger: "called Sir Roger in Sussex Arch. Soc. iii, page 89" Stemmata Robertson et Durdin page 102 Table 30
John Lewknor,  M.P. Sussex 1449, married Isabel, daughter of Sir Roger Covert 
Margaret Lewknor, married Sir john Covert  (not mentioned by Richardson in Royal Ancestry)
The Pedigree of the Early D'Oyleys in The Topographer and Genealogist gives Joan's first husband as John Deering with no issue, her second husband as Sir Thomas Lewknor of Bradhurst in Sussex whom she married in or before 1370, and the third husband as John de Cobham, esq. of Kent who was living in 1391.