I've seen some post regarding the Zilart King's descendants two of which where said to the the Archduke and his brother however it was apparently stated that there was a 3rd that was there sister the Zilart Princess.
Some have speculated that it was Eshn'ntarl but I was under the impression it was Lion? Since she possesses many Zilart features (Zilart eye's included) other than the hair. She was also discovered the same way they were she was found in the ocean.
This would require the dev's to speak about it though as I haven't seen anyone else mention this in the story.