[6] Belonging to his kinship, Gregory was unflinchingly loyal to Duke Stephen, who launched a civil war against his father, Béla IV in 1264.
However historian Attila Zsoldos argued the last mention of Gregory II is from 1256, and there is no record of him about his role in the 1260s civil war or any political relation with Duke Stephen.
[8] In the two documents, Gregory, as Judge of the Cumans – after the conclusion of the war – appeared before the elderly Béla IV in the royal court to negotiate over Slavonian estate matters with his cousins, Thomas III and Stephen II, and a distant relative, Nicholas.
In the same time, Gregory was made Master of the treasury for his sister-in-law, Queen Elizabeth (while his brother, Egidius held the same office in the royal court of Stephen V).
After Stephen's coronation, the closest advisors of the late Béla, for instance Henry Kőszegi and Nicholas Geregye, following the new monarch's sister, Anna of Macsó, fled Hungary and handed over Kőszeg, Borostyánkő (today Bernstein, Austria) and their other castles in Vas County, along the western borders to Ottokar II.
[16] Though Ottokar renounced its claims on territories conquered in Hungary, the Kőszegis, strengthening with Bohemian and Styrian defenders, refused to give back their castles along the western border.
As a result, Gregory led a royal army to successfully besiege and capture Henry Kőszegi's four castles – Kőszeg, Szalónak (Stadtschlaining), Szentvid and Borostyánkő – in August 1271.
Gregory's brother, Egidius immediately laid siege in late August to Elizabeth's estate in Székesfehérvár to "rescue" Ladislaus from the rival baronial group's influence.
The Monoszló brothers were granted the Austrian castles of Laa, Stockerau, Korneuburg and Kreuzenstein by Ottokar, who also commissioned them to administrate Pressburg and the adjacent forts.
Later, Gregory initiated the ennoblement of numerous castle warriors, who bravely fought against the invaders (e.g. in Köcsk and Káld), in the royal court of Ladislaus IV.
[23] Both Egidius and Gregory lost all political influence for uncertain reasons after 1275, as they had never hold any dignities after that, despite the fact that their allies, the Csák group was able to return to govern the realm even at the end of the year.