In the Watch Citadel within High Hall, Beorn Wunterbrood will be giving a speech to all the characters gathered during Gather Your Allies. He urges all of them to put aside their differences and unite against the greatest threat that Baldur's Gate has ever faced, before being interrupted by the entrance of the player. He is initially suspicious of the Mind Flayer within the party (no matter whether they are the player, The Emperor, Karlach, or Orpheus), but is convinced to trust them by Withers. After allowing the gathered allies to speak, and the player character to give a short speech, he announces that all these forces will be ready to join the party in battle.
Alternatively, if the party has gathered no allies for the ensuing battles, Beorn Wunterbrood will be found dead steps away from the Watch Citadel's entrance (X: 219 Y: 39). In this situation, Withers would be waiting inside to berate the party on their lack of tact and diplomatic skills, but nonetheless wish the party good fortune in the fight to come.
Despite being present in the High Hall alongside summonable allies, Beorn does not take part in the final battle and cannot be summoned via Gather Your Allies.