[SPOILERS] How to steal the Titan's Heart from the Brass Citadel?

Hi. I need to acquire the Titan's Heart from the Brass Citadel for one of the quests in the Seeker, Slayer, Survivor. However, I already blew up the Powderhouse for the endgame quest, so I can't enter the Brass Citadel without turning everyone hostile. I tried to sneak and use the Leap ability but, still, everyone gets hostile after I move past the guards.

Is there any way to get the Titan's Heart?