I hate to rain on the parade, but Yda is not royalty. Probably.

Go have another chat with Gundobald - he says Yda's father was a prominent member of the insurgency against the King of Ruin, not the King himself, and seems to have died.

Papalymo seems to regret giving Yda her new mask because she's hiding behind anonymity instead of being true to herself. Either that or said anonymity is why she's even considering joining up with the Masks, given they are clearly bad news.