One two princes kneel before you, that's what I said now.
Dark Souls 3 boss: how to beat Lorian, Elder Prince and Lothric, Younger Prince
This is it. The final Lord of Cinder. This won't irreversibly commit you to endgame, but it's a very good idea to trot round finishing any NPC sidequests you want to complete.
To reach the boss, use the shortcut lift near the Dragonslayer Armour boss arena. At the top, pause a few seconds to let the knights patrol away, giving you a clear run at the boss arena doors. The fight does not trigger till you cross the threshold at the top of the stairs, so you can take a breather here.
Good news: this is a great place for summons, and you can even bring in Sirris of the Sunless Realms if you’re offline. She doesn’t last long, but every bit helps.
Bad news: there are two bosses in this arena. Never mind, it's nowhere near as terrifying as Ornstein and Smough!
Lorian, Elder Prince kicks things off. He’s a powerful swordsman, but significantly less tricky than some you’ve met so far; his attacks are faster, but more predictable, than Dancer of the Boreal, for example. Weak to lightning and frost, Lorian isn’t too difficult a fight once you have come to understand the timings of his slashes and thrusts - and his very narrow hitbox. In general, rolling to the right is safest.
What makes things tricky is Lorian's habit of teleporting around thanks to his brother’s magic. When you see that pale corona, you better be rolling away – and you have to gamble a little that you aren’t rolling right into his slash wherever he lands. Nasty.
The second phase of the fight is much harder because Lothric, Younger Prince joins the fray. He deals out magic damage with an array of familiar spells like Soul Spear and Homing Soul Mass. He does this while mounted on Lorian’s back, so you need to tackle them both at once.
Lorian is still reasonably weaksauce, but every time he goes down, Lothric will revive him. It’s Lothric’s health bar you’re aiming to deplete. It’s tempting to rush Lothric when he’s reviving Lorian, but the revival spell does do area of effect damage, so you’ve got to be wary of that.
The easiest way to win this battle is to hit Lorian from behind; when you do that, you damage Lothric as well. Do be wary of some of Lorian’s slash attacks, which reach a long way behind him. Unfortunately Lothric’s magic means you’re never really safe anywhere.
If you need a rest to heal up, apply resin or enchant a weapon, roll away behind a pillar at the side of the room. It’s risky, because of the teleports, and Lorian’s sword will hit you through cover, but it does provide a chance to enforce some distance between you for a short time. This can also give you space for spell casting and ranged attacks, if that's your bag - but this is a very dangerous fight for those wanting to stay at a distance for any length of time.
You’ll receive the Soul of Twin Princes for your efforts, and can activate the Twin Princes bonfire.
You’re now ready to enter the true endgame. You can now either visit the very challenging optional area Archdragon Peak (also available after the final boss) or proceed to Firelink Shrine and link the flame and head off to the final boss.