Background and Marriage
Constance was the posthumous daughter of
 by his third wife
Beatrice of Rethel.
Rather strange for a princess Constance was not betrothed until she was thirty which later gave rise to stories that she had become a nun and required papal dispensation to marry.
Boccaccio related in his
De mulieribus claris that a prediction that "her marriage would destroy Sicily" led to her remain celibate. Her betrothal to
Henry was announced 29 Oct 1184 at the Augsburg episcopal palace.
 In 1185 Constance traveled to
Milan to celebrate the wedding accompanied by a grand procession of princes and barons. Henry accompanied her to
Salerno but had to return to Germany for the funeral of his mother. They were married on 27 January 1186 at Milan.
The death of her younger nephew
Henry of Capua in 1172 made Constance
heir presumptive to the Sicilian crown,
 since her elder nephew King
William II did not marry until 1177 and his marriage remained childless.
 Abulafia (1988) points out that William did not foresee the union of German and Sicilian crowns as a serious eventuality; his purpose was to consolidate an alliance, with an erstwhile enemy of Norman power in Italy.
papacy, also an enemy of the emperors, did not want to see the kingdom of southern Italy (then one of the richest in Europe) in German hands, but Henry pressed
Pope Celestine III to baptize and crown his son: the Pope put him off.