One of the more tragic Kdramas I watched recently had the same basic theme. Kid was adopted out of an orphanage to an American family. Family was very conservative and religious and the kid grew up well, enlisted in the military, rose up quickly and became a high level enlisted. He got assigned to Korea and began digging. What he found out about his life before the orphanage was really horrible. Sperm donor ran off, mom died, mom's new boyfriend dropped the kid at the orphanage and was listed as the dad. When the guy showed up in Korea, the boyfriend was in prison waiting execution for a really horrible murder.