It was to the annoyance of the pope when in 1262 her father arranged her engagement and marriage to Infant Pedro of Aragon, son and heir of King Jaime "The Conqueror". However, this also upset King Louis IX of France who then almost broke off his son's engagement to
Pedro's sister. It was only after Jaime "The Conqueror" promised never to assist Manfredo, Constance's father, that the marriage proceeded.
However, due to papal interference, Manfredo lost his crown and life in 1266. As long as Constance's father-in-law had been alive, nothing was done about Sicily; and now, even though she was Sicily's heiress, it remained in the hands of Charles of Anjou, a brother of King Louis IX of France. Her husband---who loved her dearly, and even some years before he became king---gave her in her own right the title of queen.
When her father-in-law died in 1276 he had left the Balearic Islands and Roussillon to a younger son, Jaime, who, as well as calling himself King of Majorca, for three years refused to acknowledge Constance's husband as his suzerain. In 1279 the Moors of Andalusia tried to reconquer Murcia and it took till the end of that year before the southern border was secure.

Further intrigues within the Iberian peninsula prevented King Pedro III of Aragon from pursuing his wife's rights in Sicily. In 1275 the elder son of King Alfonso X of Castile had died, leaving two young sons. Alfonso X decided to make his second son, Sancho, his heir to prevent a long minority for his grandson, the rightful heir. However, his widowed daughter-in-law, Blanche, a daughter of Louis IX of France, fled with her two sons to Pedro III of Aragon as she feared for her sons' lives.

Pedro III of Aragon welcomed Blanche and her sons but kept them as hostages. Alfonso X of Castile soon regretted his decision as in 1281 the impatient Sancho rebelled against his father.
However, in 1279 the plotting began in earnest with Emperor Michael of Constantinople and the Republic of Genoa, as these greatly feared that Charles of Anjou, the de-facto king of Sicily, might
become too powerful. On 30 August 1282, the Aragonese, with King Pedro III at its head, disembarked at Trapani for Sicily, so that the local rebellion became a European war. On 2 October Pedro III made a triumphant entry into Messina.
Nevertheless he acted most cautiously as one night a ragged old man, Vitalis dei Guidici who was once a devoted friend of King Manfredo, warned him of the inconstancy of the volatile Sicilian
nobles. Pedro III maintained that he had come to make friends with the Sicilians and not to offend them with recriminations about the past.
However, the very next day he was reminded of the warning when Lady Machalda, one of those mentioned by name by Vitalis dei Guidici, came and made it clear that she wanted to become his mistress. He escaped only by a lengthy discourse about his loyalty to his wife Constance, the rightful queen of Sicily. Lady Machalda, not a graceful loser, then induced her own husband to intrigue against Pedro III and Constance.
In the early spring of 1283 when her husband sent for her, Constance left Aragon for Sicily and, with her children---Jaime, Fadrique and Yolanda---arrived on 16 April 1283. On 19 April it was
announced that the Infant Jaime would be heir to Sicily as the elder son, Alfonso, would remain heir of Aragon. In the case of Jaime's minority, Constance would act as regent. Pedro III had to depart Sicily, leaving Constance in charge. 
Constance and her Italian-born ministers were careful to observe the rights of the Sicilians, but, soon short of money, she found it difficult to restrain the rapacious Aragonese soldiers. When Sicily was again attacked, it was only the brilliance of Admiral Roger of Lauria which saved it from an invasion. Soon the whole kingdom of Charles of Anjou was in turmoil and, with his having lost Sicily to Pedro III and Constance, riots broke out in Naples. Here, Frenchmen found in the streets were massacred.
In November 1285 Constance's husband died at Villafranca de Penadres where he was buried. His being gracious had made a good impression in Sicily but he had also been too cautious. Pope Honorious IV now decided it was time to restore peace in Italy, but also wanted Sicily returned to the House of Anjou as it had been a previous pope who had made Charles of Anjou its king.
The Sicilians, however, were distrustful of the generous promises of the pope and preferred their new king, Constance's son, Jaime, who would become known as "The Just". Jaime was about nineteen years old, whereas the new king of France, Philippe IV "The Fair", was only seventeen.

In February 1286 Jaime was crowned at Palermo. Discovering two Dominican friars sent by the pope to start a revolt in Sicily, Jaime courteously sent them back unharmed, as well offering the pope both homage and asking for the confirmation of his title. The pope's response, however, was excommunication for both Constance and Jaime---and, for good measure, all the people of Sicily as well. Constance and Jaime had reached an honourable and just agreement with the imprisoned heir of Charles of Anjou; but the pope, disallowing this, ordered an offensive against Sicily in 1287, a disastrous affair for Honorious IV.
When in 1291 her eldest son, Alfonso III "The Liberal", King of Aragon, died childless, it was Jaime, King of Sicily, who became the next King of Aragon. He remained king of both countries until 1296 when Fadrique, Constance's third son, became King of Sicily and Jaime remained King of Aragon alone. Constance, having returned to Spain, died in Barcelona in 1301.

Source: Leo van de Pas