Joan married Eustace Whitney of Whitney-on-Wye, Esq., son of Sir Robert II Whitney of Whitney-on-Wye and Gwenllian Oldcastle. (Eustace Whitney was born in 1413 in Whitney-on-Wye, Herefordshire, England and died in 1480/1.)
Sources
1Plantagenet Ancestry: A Study in Colonial and Medieval Families, Douglas Richardson, 2nd ed., 2011, p. 265.