The death of Stephen V in 1272 meant that he was succeeded by his infant son Ladislaus IV, with the widowed consort and mother of the boy, Elizabeth, as his regent. At the time, Jacob Svetoslav still held Vidin as a Hungarian vassal. Possibly in 1273, Hungarian rule in Braničevo, west of Jacob's domain, was put to an end by two Cuman–Bulgarian nobles, Darman and Kudelin. Cut off from his Hungarian suzerains and facing the menace of a Bulgarian attack from the east, Jacob Svetoslav once again submitted to Bulgarian rule. He arrived in the capital Tarnovo to negotiate his submission with Constantine's consort Maria Palaiologina Kantakouzene, who was the dominant figure in the empire at the time due to the Tsar's paralysis. There, Jacob was formally adopted by the much younger Maria as her second son, after the infant heir Michael Asen II. This adoption solidified Jacob's ties to the court and meant that he could safely retain his autonomous domain as a Bulgarian vassal. He also harboured hopes to ascend to the throne by ousting Michael when Constantine died. Suspicious of these disloyal intentions of Jacob's, Constantine's consort Maria is thought to have poisoned him, and he died in 1275 or 1276/1777, shortly before the Uprising of Ivaylo.