The oldest sibling listed in the Massarelli document was Grgur Branković. The 1429 document mentions him with the title of Despot. According to "The Late Medieval Balkans, A Critical Survey from the Late Twelfth Century to the Ottoman Conquest" (1994) by J. V. A. Fine, Grgur was appointed governor of territories of southern Serbia associated to the House of Branković. He was reportedly appointed by Murad II of the Ottoman Empire in 1439. In April 1441, Grgur was accused of plotting against Murad and his governorship terminated. He was imprisoned in Amasya and blinded on 8 May 1441. According to "Monumenta Serbica Spectantia Historiam Serbiae, Bosniae, Ragusii" (1858) by Franz Miklosich, Grgur and his brothers co-signed a charter by which Đurađ confirmed the privileges of the Republic of Ragusa. The charted was dated to 17 September 1445. According to the """" (1978) by Detlev Schwennicke, Grgur retired to a monastery under the monastic name "German". According to Fine, Grgur resurfaced in 1458, claiming the succession of the vacant throne of Serbia for himself or his son. The Massarelli manuscript mentioned Grgur as unwed. Later genealogies name his wife as "Jelisaveta". Vuk Grgurević, a son of Grgur, was later a titular Serbian despot (1471–1485). He was possibly an illegitimate.