2020-09-01 20:29:31 UTC
Most secondary sources claim that Jovan Branković, despot of Serbia (d. 1502) left several daughters by his wife Jelena Jakšić, including two who married Lithuanian noblemen and are ancestral to a large number of Polish and Lithuanian noble families. I've been vaguely aware of this for some time, and its corollary that many Poles and Lithuanians can accordingly claim descent from several Byzantine imperial houses via Jovan's grandmother Eirene Kantakouzene, but I returned to the issue recently while looking at the Princes Wiśniowiecki, descendants of one of the two daughters, and on second glance the general consensus, such as it is, seems very doubtful.
Basically, the argument seems to be this: contemporary documents name Prince Iwan Michałowicz Wiśniowiecki's (d. c.1542) wife as a certain "Marya Despotowna" or "Magdalena Despotowna" . She has then been fairly convincingly identified  as the same woman who was described as being a daughter of Jovan's wife Jelena and the wife of a certain "Prince of Visnjevac" in the sixteenth-century "genealogy of Ruvarac". It's worth quoting the relevant passage:
Po śmierci męża osta Jelena despotica, supružnica Joanna despota, sa daščerami svoimi, jeże jest sestra kneginii Glinskoj. I ona davši daščere svoje za muži, pervoju daščer svoju Mariju dade za Petra voivodu vlaškogo, a dve daščeri svoje u Litovskuju zemlu, jedinu za knezalvana Višnjevačkogo a dru[gu]ju za kneza Teodora Vladimirskoga. 
[After the death of her husband, Jelena the despotina, wife of Jovan the despot, remained with her daughters. And she gave her daughters to husbands. She gave her first daughter Maria to Peter, Duke of Vlachia, and two daughters to the Lithuanian lands, the one to the Prince of Visnjevac and the other to Prince Teodor Vladimirsky]
The problem, however, is one of chronology. Iwan Michałowicz died between 1541 and 1544, probably 1542, and Maria/Magdalena remarried Prince Aleksander Fedorowicz Czartoryski, having two further children by him and surviving until at least 1570. This seems to be pushing the envelope for the fertility of a woman who could not, in this reconstruction, have been born more than nine months after her supposed father's death in 1502. For these reasons, in 2010 Lilia Zabolotnaia proposed that Maria/Magdalena and her sister Hanna, the other daughter named by the "Genealogy of Ruvarac", were actually children of Jelena Jakšić by her *second* husband, Ivaniš Berislavić, also despot of Serbia .
I find this plausible enough, but wonder whether we should be quite so confident that the "Genealogy of Ruvarac" can be trusted even this far. It misnames the daughter Jelena who married Petru Rareș, voievod of Moldavia, as "Maria", ignores Jelena's actual daughter Maria who married Ferdinando Frankopan, and seems rather vague on the names and fates of the two daughters in Lithuania. All in all, it seems to me that the parentage of Marya/Magdalena and Hanna "Despotówna" is decidedly unproven, but I'd be interested to hear whether others have any opinions on this or could point to other contemporary or near-contemporary sources besides the ones I've mentioned.
All best wishes,
 Józef Wolff, <i>Kniaziowie litewsko-ruscy od końca czternastego wieku</i> (Warszawa 1895), 26.
 Tadeusz Wasilewski, "Przyczynki źródłowe do stosunków Polski ze Słowiańszczyzną południową w wiekach XIII-XVI", <i>Studia Źródłoznawcze = Commentationes</i> 8 (1963): 117-124.
 Lubomir Stojanović, <i>Stari srpski rodoslovi i letopisi</i> (Sr. Karlovci, 1927), 56.
 Lilia Zabolotnaia, "Câteva precizări despre dinastia Branković", <i>Tyragetia</i> 4 (2010): 115-122.