Manuel I was Patriarch-in-exile as at the time his titular seat was occupied by the Latin Patriarchate of Constantinople, and he lived in Nicaea.
Before the sack of 1204, Manuel was a deacon and hypatos ton philosophon in Constantinople.
Robert I had approached Theodore I for a peace treaty and the latter offered his daughter Eudokia in marriage to cement the deal.
Manuel I is thus reported by George Akropolites to have blocked the betrothal, twice negotiated, on religious-legal grounds: Robert, Theodore's brother-in-law, could not also become his son-in-law as this was an "illegal union" and constituted incest as it was within the third degree of kinship.
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