Prince Naka no Oe(中大兄皇子), Prince Oama(大海人皇子), Buyeo Pung(豊璋)
from "Tenji to Tenmu -Shinsetu Nihon Syoki(天智と天武-新説日本書紀)".
This manga was based on the historical evidence in the middle of 7th century(called Asuka period) in Japan.
Also there're some of fictions are mixed in this story.
According to Japanese historical record of Emperors, called "Nihon-Shoki",
Naka no Oe and Oama were son's of Jomei Tenno(an Emperor) and Kogyoku Tenno(an Empress).
In this story, Oama's father was Iruka Soga(蘇我入鹿), who was a son of noble from Soga family.
Soga clan was the most powerful family in this time.
the big brother, Naka no Oe had adored Iruka until he knew who was his little brother's father.
In fact, it was Naka no Oe's first love. Iruka was so beautiful, smart, and only Iruka was kind to Naka no Oe in his childhood.
Then, Naka no Oe knew the truth and his heart was broken.
But he couldn't hate Iruka because he was attached to Iruka deeply.
When Naka no Oe was 19 old, Pung, who was a Prince of Kudara(part of ancient Korea)
and had stayed long time in Japan, provoked Naka no Oe into "Coup d'etat".
It means planning to assassinate Iruka.
Pung wanted to remove Iruka because Iruka's policy was international harmonization.
This Prince of Kudara had to make Japanese Imperial Court an enemy against Shiragi, which was other part of ancient Korea for his national interest.
Naka no Oe and Pung pulled off "The Isshi Incident" en.wikipedia.org/wiki/Isshi_In…
and killed Iruka. Naka no Oe also thought his army killed his half brother.
But they didin't. The younger brother, who thirst for revenge on Naka no Oe and Pung, didn't die.
After 5 years later, he reappeared with very same beautiful face as his father, Iruka....
oh, too long
you can read the first part of story(Japanese) here >> big-3.jp/bigcomic/rensai/tench…
push "第一話を読む". unfortunately they didn't make English version....
This manga is serialized in "Big Comic" magazine(Shogakukan)
This Comic magazine is for men, but many of Yaoi taste are included in "Tenji to Tenmu" story