His father, Kim Yongsu (Korean: 김용수; Hanja: 金龍樹), was a son of Silla's 25th ruler, King Jinji.

When King Jinji was overthrown, all royalty from his line, including Kim Yong-su, were deemed unfit to rule over the kingdom.

Kim Yu-sin offered to have it sewn by one of his sisters; he then sent for Bohee to have it mend, but she was too nervous to come into the presence of a stranger, and politely refused by saying that "she cannot do something so small for someone so precious".

When he heard of it, Kim Yu-sin made a pile of dry logs and twigs in the garden outside of his house and set it on fire for the Queen to see.

High up on the mountain, the Queen noticed the black smoke that was coming from Yushin's residence area, and asked those accompanying her if they knew the reason.

When the Queen pressed on the issue, she finally learned from them about the rumor of Munhee's pregnancy out of wedlock and that Kim Yu-sin might burn her to death because of it.

[2] Their child grew up to be King Munmu, who completed the unification of The Three Kingdoms of Korea, 29 years after Queen Seondeok's death.

Meanwhile, Kim Yu-sin set out from Silla with 50,000 soldiers and fought the bloody Battle of Hwangsanbeol leaving Baekje devastated and unprotected.

King Uija of Baekje finally surrendered, leaving only Goguryeo to face Silla as an adversary on the Korean peninsula.