Does Fiora, Grand Duelist's ability trigger at the start of the next turn after a -might effect (like Watcher) expires, making a unit mighty again?

Ruling: Yes, Fiora's ability triggers when the -might effect expires at the end of the opponent's turn, and she will be ready again at the start of your next turn.

Sequence:

• Opponent's end of turn occurs
• Expiration phase happens (Watcher effect expires)
• Fiora's ability triggers when you have a mighty unit again
• Fiora exhausts (if you choose to pay the cost)
• Start of your turn occurs
• Fiora awakens (becomes ready)

Nuances:

• The ability triggers even if Fiora is already exhausted, but you cannot pay the cost (exhausting her) if she's already exhausted
• Exhausting Fiora is the cost to channel the rune, not an automatic effect
• Triggers go on the chain unless targeting is required and no valid target exists