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I'm not sure any such scenario has existed (proving the non-existence of something is hard), but there is what seems to be a fable:
In On the Temporal Power of the Pope: Against William Barclay (Writings on Temporal and Spiritual Authority, tr. Stefania Tutino), Β§ "The first part of the fifth argument in support of the authority of the Supreme Pontiff in temporal matters is defended"; St. Robert Cardinal Bellarmine, S.J., thinks "it is a tale that"
the marriage of the daughter of King Roger, Constance, who, even though she was a nun, from a dispensation of Pope Clement III is said to have married Emperor Henry VI.197
[translator's n. 197:] the marriage between Emperor Henry VI and Constance, daughter of Roger II, king of Sicily, celebrated in 1186 and widely contested because it could potentially have led to the unification of the Holy Roman Empire with the kingdom of Sicily.
St. Robert's refutation:
Regarding Constance, Rogerβs daughter, we think it is a tale that she, while being a nun and rather old in age, married Henry VI. In fact, Geoffrey of Viterbo, who used to instruct Henry VI in literature and in morals, writes that the marriage of Henry with Constance was celebrated in Milan in 1186 during the pontificate of Urban III, when Constance was thirty years of age. From this it follows that it would be false that Clement III or, as others say, Celestine III or, as others, Alexander III made a dispensation for her in her monastic vows; for the latter was dead already, and the others had not begun to sit on the papal throne yet. It would also be false that she married when she was old, of more than fifty years of age, and last, it would be false that she was previously a nun, since no one who lived in those times writes this. See Cardinal Baronius, volume 12 [vol. 19 of this ed., p. 546] of the Annals for the year 1186.