Child of Gavril Radomir, tsar of Bulgaria, by his Hungarian wife

As noted on The Henry Project, tsar Gavril Radomir of Bulgaria is one
of the candidates for the father of the notorious Agatha, wife of
Edward the Exile. This Gavril Radomir was married to a Hungarian
princess, daughter of Geza I and sister of Istvan I, whom he banished
while she was pregnant. He subsequently married a woman named Irene
from Larissa. Gavril Radomir died less than a year into his reign, in
1015, murdered by his cousin Ivan Vladislav.

However, a 12th century Macedonian author, Michael, bishop of Devol,
in his copy of Skylitzes chronicle, claimed that Gavril Radomir's
child by his Arpad wife was named Petar Deljan, and that he was born
in Hungary after his pregnant mother returned to her homeland. Devol
adds that this happend "during the life of Samuil", Gavril's father,
so before Samuil's death in autumn 1014. This chronology would seem to
put one nail in the coffin for the 'Bulgarian Agatha' theory, for if
Petar Deljan was the child of Gavril Radomir and his Hungarian wife,
Agatha could hardly have been the child born after the Arpad princess'
exile (unless she was a twin to Petar Deljan). If she were an older
sister to Petar, Agatha would seemingly be too old to have a daughter
who could've married in 1070/1 (Margaret of Scotland) and then go onto
produce a large family of her own.

In 1040, Petar Deljan claimed the Bulgarian throne. He quarreled with
his ally Alusian (Alousianos) son of the Bulgarian tsar Ivan
Vladislav, who blinded him in 1041. FWIW, I think Michael of Devol's
identification of Petar Deljan as the child of Gavril Radomir seems
sound; if he were not, it seems bizarre that a foreigner (as Deljan
was born and raised in Hungary) could've gotten as far as he did
unless he had a strong blood claim to the Bulgarian throne. Certainly
someone like Alusian, who had a claim through his own father, would've
known if Petar Deljan was a fake or not and there would've been no
reason for him to ally with him, even initially.

Source: J. Prokic, 'Die Zuzatse in der Handschrift des Johannes
Skylitzes: codex Vindobonensis hist. graec. LXXIV: Ein Beitrag zur
Geshichte des sogennanten westbulgarischen Reiches' (Munich, 1906).
.