His cousin used to live next door. There are remarkably few of them left ~ just like someone went hunting for them eh.
http://www.iht.com/articles/2006/05/19/news/profile.php
http://en.wikipedia.org/wiki/Yi_royal_family
No offense to your friend, but I doubt the story. 15% or more of Koreans have the surname Yi (spelled Rhee or Lee sometimes). The particular clan of Yi that became the Korean royal family is smaller, but still very numerous. I have an aunt who is from this family. The Japanese dealt with the Yi family by having the Empress killed, but did not engage in a widespread extermination of the family. The next in line was forced to become a Japanese prince and live in Japan. The Japanese did many wicked things in the 20th century, but did most of the really terrible things to the Chinese, whom they considered subhuman. The rationale that was used to annex Korea was that Koreans were a related people, which is certainly true.