"Diego, did you know that there is a blue king in this world?"
"Not only the blue king, but I also know Aunt Katie was the red queen."
"You remembered it?"
Back when Chleo and her family went on vacation to Germany to visit Katie, she vaguely overheard an adult's conversation saying Katie was the red queen and so on. At that time, Diego was still very young and couldn't even speak fluently, so she didn't think Diego would remember something from years ago.
"A little." Diego had no recollection of the kidnapping or anything when they were in Germany. He only remembered events that had happened in his previous life.
And Diego remembered, his father had told him that Katie, the red queen, had given a life energy transfusion to Chleo in exchange for her life. That's where he found out the existence of the red king. But he had no idea that there were other rulers besides the red queen.