Cuan

“Don't forget, Sigurd. I'm always here for you. Especially in times like these.”
— Quan, to Sigurd

Quan (Japanese: キュアン Cuan) was the prince of Leonster, the son of King Calf, the father of Altena and Leif, a full-blooded descendant of the Crusader Njörun, and the inheritor of Gáe Bolg. In his youth, he was educated at the Belhalla military academy, where he met Sigurd of Chalphy and Eldigan of Nordion; the three quickly became close friends and pledged each other's support in times of need, and Quan eventually married Sigurd's sister Ethlyn. When he received word of the Verdane assault on Grannvale in Grann 757, he departed Leonster with Ethlyn and the young knight Finn to assist Sigurd, and travelled with him through Agustria to Silesse.

While Sigurd was in exile in Silesse, Quan departed Sigurd's group to return to Leonster and raise reinforcements to assist him, and on his way through the Yied Desert to do so, he and Ethlyn were besieged by the Thracian dragon knights and were killed, in what became known as the Yied Massacre. Though he was never formally crowned during his life and in fact was killed before his father, years after his death he was nonetheless referred to as "King Quan" as an honorary title.

(Source: Fire Emblem Wiki)