The series confirms Brynden Rivers was one of the Three-Eyed Ravens.
Also known as Bloodraven, Brynden was the bastard son of King Aegon IV Targaryen and Melissa Blackwood. He remained loyal to the Targaryens during the Blackfyre Rebellions, later serving as Hand of the King and Lord Commander of the Night’s Watch.
A rumored sorcerer and lover of Shiera Seastar, Brynden eventually became the legendary Three-Eyed Raven.