Lorian, Elder Prince and Lothric, Younger Prince

Lorian, Elder Prince and Lothric, Younger Prince, also known as the Twin Princes, are a pair of bosses in Dark Souls III.

Description
Lorian is a knight with a pale skin and long silver hair, armed with a flaming greatsword. He is mute and crippled, unable to stand on his legs for more than a second. He is much larger than his sibling, Lothric.

Lothric appears frail with thin pale arms and long fingers, he wears a black robe and during the second phase he will teleport down and hold on to his brother's back.

Location
They are found at the top of Lothric Castle after clearing the Grand Archives, at the end of one out of the two big bridges that are visible from the High Wall, there's a shortcut elevator shortly before their arena.

There are two accessible elevator shortcuts to this boss, the first being immediate to the Grand Archives bonfire, and the most obvious. The second, being in the room outside of the Dragonslayer Armour boss fight; this elevator puts the player closest to the Twin Princes' boss area.

Lore
Lothric and Lorian (along with Ocelotte) are the sons of King Oceiros and the queen of Lothric (possibly Gwynevere), they are said to be inseparable due to a curse, when the bell tolled to signify the fading of the flame, they rejected their duty to become Lords of Cinder and watched the fire fade from a distance.

Lothric may have never actually become a Lord of Cinder despite having a throne dedicated to him in Firelink Shrine; he wasn't resurrected nor did he abandon his throne like the other Lords, he never took his throne in the first place. There are several points in the game that confirm this: The only counter-argument to this theory is the "Lord of Cinder Fallen" message upon their defeat, but that might be because he was destined to be one.
 * 1) They are not mentioned in the opening cutscene.
 * 2) The description of their soul implies they never became Lords of Cinder.
 * 3) Lothric still has his sanity, something that most dead/hollow and resurrected beings in the Dark Souls universe lack, suggesting he never died.
 * 4) After returning all Cinders of a Lord to their thrones, Lothric's head is the only one that still has its flesh.

Note: There is a theory that the royal family of Lothric wanted to create the perfect Heir to the Fire but failed, which is why Lothric is cursed.

Fight overview
The scene starts with the Ashen One opening the gates to the court room, located at the highest point of Lothric Castle after making their way out of the archives. As they approach the throne, an ominous and infirm-looking figure greets them from above; Lothric, younger of the Twin Princes. He tells how he has no interest in fulfilling his duty as a Lord of Cinder, preferring not to intervene and instead see the flame fade into nothing. Meanwhile, a larger figure slowly crawls in from the shadows. Barely being able to move due to him being crippled, Lorian, the elder brother, prepares for battle.

As the encounter starts, Lorian makes it clear that his inability to walk is no impediment to him being a worthy adversary. As his first move, he will teleport near the player and slam his fire-imbued greatsword into the ground. His attacks are, for the most part, easy to evade and he turns around slowly, allowing the opportunity to score some hits on him. He may retaliate by unleashing a back-swipe with his greatsword to keep punishment at bay, though.

Soon enough, Lorian will teleport and disappear from view, preparing his next attack. He will reappear somewhere in the court room, away from the player. It is of utmost importance to locate his position as soon as possible and prepare to roll to either side. He will rise his greatsword, building up power, and unleash a devastating holy ray across the room in the player's direction. The attack is so powerful that it will deplete about ¾ of a full HP bar of a player with about 30+ Vigor and equipped with very good armor, so avoiding it should become a priority when the time comes.

Once Lorian has been subdued, another cutscene will take place with Lothric coming down from his bedstead to aid his brother, imbuing him with new life and then climbing onto his back. The battle will recommence then in almost the same manner. Lothric will be casting small magical homing projectiles throughout the course of the fight. Each of these will inflict only a small amount of damage, but if the player is caught in the full barrage, it could prove to be fatal. Additionally, Lothric will occasionally cast a variant of Soul Spear during the fight.

One of the most notable differences in this phase, however, is that when Lorian unleashes his great holy ray, Lothric will follow it with a casting of Soul Spear, which may take overconfident players by surprise.

Each brother has his own boss health bar, making them independent of each other. The player may opt to attack either one. However, if Lorian falls first, Lothric will climb down from his back and hurry up into reviving him. This will leave him completely vulnerable to the player's attacks for a short period of time. If he succeeds, however, he will trigger an area-of-effect explosion and Lorian will be given some life back and continue the battle.

If the player manages to kill Lothric first, then the fight will end and Lorian will fall to his death automatically. However, this may prove to be somewhat difficult, as hitting Lothric is not as easy due to Lorian constantly turning around.

Strategy

 * Lorian is an enemy classified as wearing a metal armor, and as such, Lightning does increased damage against him; Gold Pine Resin or the Lightning Blade miracle are highly advised.
 * If entering the arena via fog door (if either the player died previously or if they exited and continued the game during the encounter), Lorian will always start the battle by teleporting near the player and attack them with his greatsword. However, if the player remains in place as they enter, when he teleports, he will end up doing so near his initial location, giving the player the option to start the encounter in a less compromising way.
 * During the battle, be wary when using the auto-lock to target Lorian. When he teleports into a ray of light, the lock-on will disengage and Lorian will reappear and attack, while the player may be searching for him.
 * Using a short sword/long sword is preferred to use against Lorian, because of his teleporting attacks. Using a great sword may have some issues, preferably used if you're going in with other phantoms.
 * During Lorian's second phase, when he slowly raises his sword to slam it back to the ground, remember to dodge this attack once its starts while also remembering to dodge Lothric's light beam (where if Lorian's attack didn't hit the player, then Lothric's will, and could possibly prove fatal).
 * During the second phase, use a weapon with a long reach, such as a greatsword, and attack Lorian from behind, this will also damage Lothric which normally would only be possible when he revives his fallen brother.

Trivia

 * Prince Lothric could be considered the primary antagonist of the game, as most of the catastrophic events happening during the course of the story are due to his stubbornness and unwillingness to assume his duty to link the fire. As the figure with the highest power in Lothric, he proved to be a very inefficient leader, as his kingdom was left in total chaos and disarray, being invaded by the powerful forces of the much more organized Irithyll of the Boreal Valley under orders from Sulyvahn who presumably intended to feed them to Aldrich.
 * Prince Lothric is voiced by Harry Lister Smith, who also voiced Dark Sun Gwyndolin from Dark Souls.