Donald M. Nicol, The Byzantine Family of Kantakouzenos (Cantacuzenus) ca. 1100-1460: a Genealogical and Prosopographical Study (Washington, DC: Dumbarton Oaks, 1968), p. 188. Nicol had originally believed that Demetrios I Kantakouzenos was the father of Helena and George, though later abandoned this theory, stating that it is more convincing that Theodore was the father; see his "The Byzantine Family of Kantakouzenos: Some Addenda and Corrigenda", Dumbarton Oaks Papers, 27 (1973), pp. 312f
