I think maybe WwW and Leo were in love, but for political reasons he married Eva? WWW and Cora became friends, each wanting to kill Eva, but then Cora had Regina marry Leo. And Regina killed Leo. That would be a reason for revenge?
But Leopold seemed like he was head over heels in love with Eva when we met him Fruit of the Poisonous Tree. If anything, he was supposed to marry WWW for political reasons but chose love and Eva over politics.
What if WWW and Leo were in love … and Leo intended to follow his heart and marry her … but Eva wanted him and went to Cora for a love potion? Cora would adore having her hated rival in her debt.
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“Though lovers be lost love shall not;
And death shall have no dominion.”
-- Dylan Thomas