Following the death of her husband, Tomasina's brother Albertino Morosini took over the upbringing of the child Andrew. The uncle ensured Andrew's rights to the inheritance of Stephen's first wife, Isabella Traversari, daughter of a powerful
Ravennate family. Tomasina supported her son's claim to the Hungarian throne. Upon the invitation of some Hungarian lords, Andrew, adopting the title of
Duke of Slavonia, acted as a pretender to the throne against
Ladislaus IV of Hungary () in 1278 and 1286–1287, adopting the title Duke of Slavonia, but he soon returned to Venice after the unsuccessful attempts. Following the murder of Ladislaus IV in July 1290, Andrew remained the last male member of the Árpád dynasty. He was elected and crowned king of Hungary shortly thereafter, but it took him more than a year to consolidate his power against
Albert I, Duke of Austria and the rival claimant
Capetian House of Anjou. , the reverse of which (right) depicts the king and his mother Tomasina facing each other with the queen mother's initial "M" Andrew III invited his mother to Hungary following the ratification of the
Peace of Hainburg which concluded the 1291 Austrian–Hungarian war. Meanwhile, the Republic of Venice decided to send an official delegation to Hungary, headed by her maternal uncle,
Giovanni Cornaro, to accompany Tomasina to the kingdom in September 1291. It is possible that Andrew's former tutor,
Marco da Saliceto belonged to Tomasina' entourage too. The Venetian ships were heading for
Zadar, where the delegation of
Trogir would have joined them and the local citizens paid homage to Queen Tomasina. However, the ships of the delegation spent a long time wandering off the coast of
Dalmatia in the following months, because of the piracy activity of the
Šubići, partisans of the rival Angevins. In May 1292, the Great Council instructed the delegation, that if they cannot continue their journey within weeks (it is plausible that they were unable to leave Zadar securely), they should return to the lagoons of Venice. The delegation was finally able to continue their journey and Andrew III sent his confidant
Ugrin Csák to
Primorje in order to escort his mother Tomasina to Hungary, but he was captured and imprisoned by certain "disloyal barons". He was freed from captivity by
Radoslav Babonić upon the king's order, and Radoslav also accompanied the queen mother to
Zagreb in July 1292, where Andrew III and his royal army joined them after the suppression of the
Kőszegis' rebellion. Initially, Tomasina had no official political role in Andrew's court and she was frequently styled as simply "the king's mother" () in 1293. Nevertheless, she took part in decision making from the very beginning as one of the royal advisors of her son. Her position and legal claim was strengthened by the fact that silver
denarii were minted with her initial letter "M" and a crown shortly after her arrival to Hungary. Among these coins, three varians are known, two of them depicts the king and his mother (with crown) facing each other, between them a cross with the crown and letter "M" at the bottom. Although she was never crowned formally a "queen mother", a separate queenly court had established around her person. For instance, she had her own count of the court (
Atyusz Hahót), treasurer (
Dominic Csák then Ladislaus Péc), chief steward (
Lawrence Kórógyi) and cup-bearer (
John Péc). Andrew III donated the queenly estate of
Segesd in
Somogy County and other possessions to Tomasina to cover the costs of her household, thus she benefited from the traditional queenly possessions. Only a non-authentic charter refers to her as "Duchess of Whole Slavonia and Lady of the Maritime Province" () with the date 1293. In this document, Andrew III made a gesture by naming
Paul Šubić the hereditary
ban of Croatia and Dalmatia on condition of faithful service to the king and his mother. Its authenticity is accepted by some Croatian historians. She styled himself simply "the king's mother" still in early 1295, when donated the estate
Szob – a portion of the Segesd lordship prior to that – to
ispán Ladislaus Tengerdi.
Duchess of Slavonia According to historian Tamás Kádár, Andrew III entrusted her mother to administer the southwestern parts of the realm sometime in 1293. Dániel Bácsatyai considered that it occurred only in 1295. She first appears in this dignity in November 1295, when confirmed the ownership right of
Conrad Győr over
Geresd against the claim of
Benedict, Bishop of Belgrade. Attila Zsoldos considered that Tomasina was created duchess sometime between April and November 1295, but already in 1294 there was an attempt to do so. Tomasina's full title was the "Duchess of the Whole of Slavonia and the Governor of the Provinces from the Danube to the Adriatic Coast" (); her duchess province covered the region "Slavonia" between the rivers
Danube and
Drava, through from
Gvozd Mountain to the
Adriatic Sea, while she administered the remaining attached territories with the title of governess. Soon, her court was established consisted of her original entourage from Italy and local Hungarian lords. For instance, she donated a customs place with the consent of her "own barons" in 1295. in
Slavonia, Duchess Tomasina's seat Tomasina ruled her province with sovereign authority and was mandated to defeat those powerful local lords who had aspirated to establish
oligarchic domains in the region. Tomasina held her provincial seat at the fortress of
Požega. Her jurisdiction extended to
Baranya and
Tolna counties in
Transdanubia too. Tomasina's activity jeopardized the interests of Ugrin Csák, the most powerful lord in
Upper Syrmia, who held
Syrmia and
Valkó counties firmly under his control, but Tomasina's duchy prevented his western expansion into
Požega County. Tomasina's maritime province was also an area of permanent interest to the Republic of Venice. According to Slovak historian Martin Štefánik, the inhabitants in Dalmatia spoke to close to
Venetian dialect, and local traditions and mentality (e.g. municipal autonomy) were also adopted from Venice, thus Tomasina was able to represent her son's interests by navigating the local conditions. In addition to Venice, the rival Angevins also attempted to build a circle of supporters in the region by contacting with the Dalmatian coastal cities. Her appointment as Duchess of Slavonia caused opposition and rebellion among the local lords, but Tomasina proved to be a strong mainstay of the royal power. The Muslim-born brothers
Mizse and
Eyza, former partisans of the late Ladislaus IV, were among the local landowner nobles, who rebelled against Tomasina's rule. Eyza plundered the region of Baranya County, his men, John and Paul Véki, looted and destroyed Tomasina's personal estate Danóc (present-day a borough of
Gajić in
Croatia) too with its nearby monastery in Gecs, both defended by Provost
Andronicus of Veszprém. Eyza and his men caused a damage of 1,000
marks to the provost, while his several servants were robbed or killed. Around the same time, in 1294 or 1295, Mizse occupied by force the royal fortress at
Dunaszekcső and he refused to return it to the monarch or his mother. In response, Tomasina Morosini recruited an army;
Palatine Nicholas Kőszegi,
Paul Balog, Bishop of Pécs and Ladislaus Tengerdi also participated in the military campaign. Tomasina's troops successfully besieged and took the fort from Mizse. Thereafter, she handed over the fort to Andrew III. Radoslav Babonić also rebelled against the duchess in the same year; as a result she besieged and captured his castle of Orbászkő (ruins near present-day
Vrbaška,
Bosnia and Herzegovina). Tomasina also sent a reinforcement unit to the royal army of Andrew III, who marched to
Tiszántúl to defeat
Roland Borsa, the powerful
Voivode of Transylvania. ==Death and legacy==