Bryennios 3 was the son of Tourkos (i.e. Bardanes 3): Petrus, Vita Ioannicii 16 (τῷ υἱῷ τοῦ Τούρκου, τοὔνομα Βρυένης). He was a cousin of the emperor Leo V (Leo 15): Sabas, Vita Ioannicii 16 (οὖ ἀδελφιδὸς πέλων τις συγκλητικός, Βρυένης ὀνομαζόμενος), Petrus, Vita Ioannicii 16 (they were exadelphos and adelphidos of one another). Bryennios 3 (Bryenes) used to visit Ioannikios 2, who on one occasion prophesied in a riddling manner that Leo 15, who was at that time strategos, would become emperor: Sabas, Vita Ioannicii 16, Petrus, Vita Ioannicii 16.

After Leo 15 became emperor, Bryennios 3 told him the story and he sent Bryennios 3 back to ask Ioannikios 2 about the length of his reign; Ioannikios 2 would only reveal that Leo 15 would persecute the church; at this meeting Eustratios 19, Petros 126's informant, was present: Petrus, Vita Ioannicii 17. The date is presumably 813. Bryennios 3 was a brother or half-brother of Barka 1.

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