I keep thinking back to to episode 1×13 What Happened to Frederick in which Prince Charming volunteered to defeat the siren of Lake Gnostos (who could be the “Lady of the Lake”). The siren resembled Snow White so as to tempt Prince Charming, and he slayed the siren and lost his sword at the bottom of the lake. Could the sword be Excalibur? Perhaps the sword was lost to time but Rumpel somehow retrieved that which was lost from the magical lake, because we know Mr. Gold had it in his pawn shop in the season 1 finale.
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy