A modern researcher has suggested that this Joan was in fact the daughter of  Robert Waterton, Constable of Pontefract Castle and her mother was Cecily Fleming.  Cecily Fleming was the heir in her issue (Joan) of her father Sir Robert Fleming of Woodhall Methey.  Cecily had a brother Robert Fleming, dean of Lincoln who apparently dsp.
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Here's a design for a Fleming ancestry:

   1 William de Flandresis
   2 Reyner I le Dapifer le Fleming at Wath on Dearne abt 1125
   3 William I /II dead by 1166, recieved manor of Clifton
   4 Reyner II dead by Michaelmas 1205, Founder of Kirklees Priory
   5 William II / III  died before 1234
   6 (brother) John I died by 1250 (Early Yorkshire Families)
   7 Reyner III Fitz john died by 1300 married Eglantine (or Rosamund)
       de Horbury (EarlyYorkshire families)
   8 William III/IV granted a fair at Wath-on- Dearne by Edward I in
       1302
   9 Reyner IV (son or brother?) granted a fair at Wath-on- Dearne by
       Edward II in 1312
   10 John II (probably son ) granted a fair at Wath-on- Dearne by
       Edward II in 1316, was He the John le Fleming who witnessed a
       Thornhill deed in 1325 ?(Thornhill of Thornhill post by John R.)
   11 Thomas I Lord of Clifton in 1344 ( Ibid Thornhill of Thornhill
       post)
   12 John III married Joan Fauconberge d 1356 (John R .`s post)
   13 Thomas II( had younger brothers Lambert who took the name Watts
       and Reyner (Watts website)
       ( one or two unknown generations ? )
   ? 14  John  IV Fleming , last Fleming feudal lord of Wath on
        Dearne, Clifton. etc( John R`s post
     15 Cecily Fleming born say 1390  or earlier married 1407/08
         Robert Waterton, uncertain if a daughter of Thomas II,  John
         IV or another Fleming of this house.
          Note, if relationship is not otherwise stated, I believe each
          generation to be father to the suceeding one.
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