As discussed by Gordon McDaniel in his article 'On Hungarian-Serbian
Relations in the Thirteenth Century: John Angelus and Queen
Jelena' [Seattle (Wash.), published Ungarn-Jahrbuch Band 12,
1982-1983, München. page 43-50.], the marriage license of Anseau de
Cayeux and his wife Maria names Maria as the daughter of „Calojohanni”
and „imperatore Constantinopolitano, eiusdem Matildis avunculo”; the
dispensation for the same marriage identifies her mother as „Matildis
dominæ de Posaga, natæ comitissæ Viennensis”, that is, Mathilde,
daughter of Marguerite de Courtenay (the sister of the Latin emperors
Robert and Baldwin II) and Heinrich, count of Vianden.

Helena, the queen of Uroš of Serbia, is described by Akropolites as
being born of „Ungariæ regis generum”, or if you prefer the Greek,
„ton Hroson Ourov, tou regos Ougrias epi thygatri telounta gambron”,
implying that the Hungarian king was Uroš' father-in-law. McDaniel
points out that neither Andras II nor Bela IV had daughters that can
be identified with Helena. The biographer Danilo II, archbishop of
Serbia, writing in the early 14th century, says that Queen Helena was
from a French family („ot plemene fruskaago”) while a continuator of
his work adds that she was of imperial descent („ot plemene carska”).

On other occasions Charles I of Sicily and Charles II of Sicily
addressed the sisters „Jelena et Maria de Chau” in various documents
as „consanguinea nostra carissima, cognata nostra, affinis nostra
carissima”, etc. Helena is identified in one document as „Regine
Servie karissimorum consanguineorum nostrum”. McDaniel's hypothesis is
that „Maria de Chau” was the wife of Anseau de Cayeux (who served
under Charles I) and that Helena her sister was the wife of Uroš. For
more on the Angevin documentation of the sisters, see McDaniel's 'The
House of Anjou and Serbia', in 'Louis the Great: King of Hungary and
Poland' (1986).

I will attempt a basic chronology of Kaloioannes Angelos, lord of
Srem, his wife Mathilde, and their daughters.

Kaloioannes himself was well attested as the son of the Byzantine
emperor Isaakios II by his marriage to Margit of Hungary, daughter of
king Bela III. As his mother was only nine or ten at her marriage in
1185, he was probably born no sooner than 1190, and likely around
1195, when his father Isaakios was deposed and blinded by his own
brother, the usurper Alexios III Angelos. Constantinople fell to the
Fourth Crusade in 1204 and Kaloioannes' widowed mother married the
Crusader lord Bonifazio of Montferrat, became queen of Thessaloniki,
and gave birth to another son by this second marriage, Demetrios.
Bonifazio was ambushed while campaigning against the Bulgarians and
killed in 1207. Margit, now a widow for a second time, married Nicolas
de St. Omer and had more children with him.

In 1222, Margit's brother Andras II gave her lands in Srem. McDaniel
suggests she had by then returned to Hungary and likely took
Kaloioannes with her. By this time Andras II was married to Yolande de
Courtenay, the niece of the Latin emperors Baldwin I and Henry,
daughter of the would-be emperor Pierre de Courtenay, and sister of
the emperors Robert and Baldwin II.

Mathilde von Vianden was a daughter of Marguerite de Courtenay, a
sister of Yolande the queen of Hungary, by her husband Heinrich von
Vianden. It it unknown under precisely what circumstances the marriage
between Mathilde and Kaloioannes came about. My theory is that she was
sent to the Hungarian court to attend on her aunt and make a good
marriage there. Here is where the chronology gets tight.

Mathilde's maternal grandparents, Pierre de Courtenay and Yolande of
Flanders, married in summer 1193. Her mother, Marguerite, seems to
have been the eldest daughter (she is named in Baldwin II's testament
of 1247 as the next heir to Namur after his own son Philippe) and may
have been the oldest child of Pierre and Yolande's marriage. But the
earliest Marguerite could've been born was spring 1194. Marguerite was
already a widow and married for a second time to Heinrich, count of
Vianden, in 1216. By 1227, Kaloioannes seems to have been politically
and militarily active, as the pope had written to him imploring him to
move against Bosnian heretics, and he was in possession of Srem by at
least 1235. Both Helena and Maria married between 1250-1253 and became
having children. Helena's eldest son Dragutin was old enough to marry
about 1268. It seems that Helena and Maria must've been born between
1227-1235 (it is tempting to suppose that Helena's godmother was Elena
Mstislavovna of Novgorod, wife of Kaloioannes' cousin Prince Andras of
Hungary).

1193: Marriage of Pierre de Courtenay and Yolande of Flanders.
c.1194: Birth of Marguerite de Courtenay
c. 1195: Birth of Kaloioannes Angelos
1215: Yolande de Courtenay marries King Andras II of Hungary
c. 1215: Marguerite de Courtenay marries Heinrich, count of Vianden
c. 1216: Birth of Mathilde von Vianden
1217: Pierre de Courtenay captured by Theodoros of Epiros as his army
goes overland to Constantinople, and is never heard from again
1219: Yolande of Flanders, now empress regent in Constantinople, dies
1222: Margit of Hungary granted Srem
c. 1230: Marriage of Kaloioannes Angelos and Mathilde von Vianden.
About this time or a little after Margit either dies or surrenders
Srem to her son.
c. 1232: Birth of Helena Angelina of Srem
c. 1235: Birth of Maria Angelina of Srem
1243: Uroš becomes king of Serbia after his brother Vladislav is
deposed
c. 1250: Helena marries Uroš of Serbia
1253: Maria marries Anseau de Cayeux
1276: Dragutin grants his mother Helena an appanage based in Shkodra
(now part of Albania)
1280: Charles of Sicily grants travel documents to Maria, wife of
Anseau de Cayeux, so she may travel with her son from Apula to Serbia
to visit „her sister the queen of Serbia”.
1281: Charles of Sicily issued authorization for „Maria de Chaurs” to
return from Serbia with an emissary from the Serbian court, a nobleman
named George
1282: Dragutin, son of Helena and Uroš, claims the title 'king of
Srem'.
1285: Last documented appearance of Maria Angelina of Srem, widow of
Anseau de Cayeux

Druga hipoteza bila bi da je Jelena bila kći Raula od Kurtnea, kneza od Kijeti i njegove žene Alise de Monfor. Ovo je zasnovano na tome što Farlati govoreći o Mariji, Jeleninoj sestri, kaže da je bila „ de domo Chieriz de Francia”, ali u jednom trenutku „ de domo de Chiutiz de Francia”. Ovako napisano, ovo Chieriz ili Chiutiz govori da je to njen roditeljski dom. Utvrđeno je da ovakva francuska porodica nije postojala, ali postojala je „de domo de Chieti ”. Raul de Kurtne bio je u to doba knez od Kijeti, a isto tako bio je brat od strica Balduinu II, te bi Balduin II bio Jeleni i Mariji stric, a francuski kralj Luj IX i Karlo Anžujski malo dalji rođaci. Jolanda de Kurtne, sestra od strica Raulu de Kurtneu i sestra cara Balduina, bila je treća supruga ugarskog kralja Andrije II. Mijatović odatle izvodi srodstvo Jelene i ugarskog dvora, gde su u Budimu verovatno došli svatovi srpskog kralja i odveli je u Srbiju.