Correct me if I'm wrong but I believe he's the first foreigner to appear on KOMS. For those of you who don't know Milijenko Matijevic is the singer of the 90s rock band Steelheart. You may have heard their song She's Gone before since it's popular in Korea and was even covered by a duo named Norazo (second slide). There's also a pterodactyl version (turn the volume down if you listen to this version!!!). Anyways, his performance gave me (and Cheetah) chills.
His pronunciation is actually really good!! Someone in the comments said that he started preparing four months prior to being on the show, but still...The song is Im Jae Bum's Confession by the way.