Her name and parentage are recorded by William of Tyre. The Lignages d'Outremer name "Costance" as daughter of "Beymont…prince" and his wife, recording her marriage to "Reimont le fill au comte de Poitiers".
She succeeded her father in 1130 as CONSTANCE Pss of Antioch, under the regency successively of her mother, her maternal grandfather and her mother’s brother-in-law Foulques d'Anjou King of Jerusalem. Her succession was challenged by Roger II King of Sicily, as nearest male heir, but he was unable to press his claim due to more urgent business in southern Italy. "Fulco rex Hierosolymitanus rector ac bajulus principatus Antiocheni filiæque Boamundi II iunioris" confirmed a donation to the church of the Holy Sepulchre by charter dated Sep 1134. Her first marriage was arranged by Foulques d'Anjou King of Jerusalem, in secret from her mother who had offered her hand to Manuel Komnenos, son of Emperor Ioannes II.
She succeeded her mother [after 1136] as Lady of Latakieh and Jabala. She rejected three potential candidates as her second husband proposed by Baudouin III King of Jerusalem: Yves de Nesle Comte de Soissons, Gauthier de Fauquemberghes Châtelain de Saint-Omer, and Raoul de Merle. She also rejected Ioannes Dalassenos Rogerios [Jean Roger the Norman] who had been proposed by Emperor Manuel I. "Raimundus I princeps Antiochenus" donated property to the church of the Holy Sepulchre, with the consent of "uxoris Constantiæ", by charter dated 19 Apr 1140. William of Tyre records her second marriage. The Lignages d'Outremer name "Rinaldo de Castellion" as second husband of "Costanza…la Nova Princessa". When her second husband was taken prisoner in 1160, Constance claimed that power in Antioch had reverted to her. However, Baudouin III King of Jerusalem declared her son Bohémond as the rightful prince under the regency of Patriarch Aimery. Constance appealed to Emperor Manuel I, who sent ambassadors to Antioch to negotiate a marriage between her daughter and the emperor, their presence alone being sufficient to re-establish Constance's rule in Antioch. Following riots in the city, Pss Constance was exiled in 1163 and her son installed in her place. Runciman specifies that Constance appealed to Konstantinos Dukas Kalamános as Governor of Cilicia for help when she was exiled, but this appears incorrect as Kalamános was only appointed Governor in 1167.
Her date of death is not known, but in a charter dated 1167, her son called himself "Prince of Antioch, Lord of Latakieh and Jabala" which was his mother's dower, implying that she had died by then. Bohémond III Prince of Antioch confirmed donations to the church of St Mary, Josaphat, confirming that "mater sua Constantia, frater Raynaldus et soror Philippa" were buried there, by charter dated Sep 1181. 2
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