[3] Chronologically, he first appeared in contemporary records when, under the banner of Duke Stephen, participated in the royal campaign in the summer of 1253, when King Béla IV launched a war against Ottokar II in Moravia and laid siege to Olomouc.

He fought against the Byzantine Empire with his own army corps in 1263, when Duke Stephen sent reinforcements under the command of Ladislaus Kán to Bulgaria to provide assistance to Despot Jacob Svetoslav.

[4][5][6] The tense relationship between Béla IV and Stephen – who adopted the title of "younger king" and ruled the eastern part of Hungary – sparked into a civil war at the end of 1264.

Around 10 December, brothers Ladislaus and Julius Kán, who defected to the senior king shortly before, invaded Duke Stephen's realm along the valley of Maros (Mureș) river and occupied contiguous lands in southern Transylvania despite the failed efforts of Alexander to regain these territories.

[7] Although Stephen defeated the army of the Kán brothers, the simultaneous attack of his province in Northeast Hungary forced him to retreat as far as the castle at Feketehalom (Codlea, Romania) in the easternmost corner of Transylvania.

[8] He was among the few defenders during the siege of Feketehalom, when the advancing royal army of Béla under the command of Lawrence, son of Kemény began to besiege the fort in the last days of December 1264.

The fortress was first attacked by an army vanguard led by Conrad, brother of Lawrence, who tried to break through the castle gate with a rapid advance, but Alexander and his soldiers prevented this.

[13] Alexander's involvement in the civil war and loyalty to Duke Stephen served as a point of reference in the judicial court of Dowager Queen Elizabeth of Poland almost a century later – in 1353 – concerning the estates of the extinct Edelényi (Karászi) family which returned to the Crown, that already their ancestor Alexander should have been deprived of all his possessions as a result of his rebellion against the rightful ruler Béla IV, so that all their possessions of his descendants, the Edelényis, who died without male descendants, were already illegal.

[15] After the restoration of the Hungarian rule over the Banate of Severin (Szörény) following Stephen's successful Bulgarian campaigns, Alexander was styled as ban of the province in 1268, but he was replaced by Ugrin Csák in this dignity already in the same year.

[16] For his loyal service and military merits, Alexander was granted the villages Kazinc (today a borough of Kazincbarcika), Ludna and Harica in Borsod County by Younger King Stephen in 1267.

[5][20] According to historian Attila Zsoldos, the creation of the new institutions of provincial jurisdiction, namely the "noble judges" (judices nobilium) occurred during the term of Alexander against the power aspirations of Queen Elizabeth.

[21] Alexander was dismissed as Judge royal and ispán of Vrbas County by Ladislaus Kán and Lawrence, son of Kemény, respectively, when Elizabeth attempted a self-coup during Ottokar's invasion of Hungary in the spring of 1273.