Captured Crown Prince

As an Emperor, he was held hostage by the rival prince after his empire was destroyed. The Prince threatened to bring him back to the Eastern Palace and keep him as a slave. He thought he would be a miserable prisoner... However, even though the Prince would humiliate him when he was angry, most of the time, the prince showed great tolerance to him and gave him countless privileges. "What did the Prince mean when he mentioned 'our past' ?" “Why can't I remember anything...?”