Board Thread:General Discussion/@comment-29970809-20170806002834/@comment-28895263-20170807053536

Euron has also said (at the Kingsmoot) "give me 1,000 ships, and I will give you this world". At the time, he was going to start by marrying Daenerys, and deposing Cersei. That does not sound like a loyal subject of the crown to me.

Euron's loyalty is situational, and temporary. That's what Yara and Theon told Daenerys in Mereen (Season 6) and what Cersei and Jaimie acknowledged to each other (S7E1).

Euron's Oath of Fealty isn't worth the parchment it's printed on.