Did you save his daughter in the Iron Throne?
I think if you do, you gain control of him for the second battle and he waits outside the room for the Titan fight.
Otherwise Hold Person + Sanctuary should work.
Baldur’s Gate 3 is a story-rich, party-based RPG set in the universe of Dungeons & Dragons, where your choices shape a tale of fellowship and betrayal, survival and sacrifice, and the lure of absolute power. (Website)
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Did you save his daughter in the Iron Throne?
I think if you do, you gain control of him for the second battle and he waits outside the room for the Titan fight.
Otherwise Hold Person + Sanctuary should work.