I also think he read about it in the book, but obviously it doesn’t figure in his own story of Peasant Rumple becomes the Dark One. Nor would it be in “Rumplestilskin” and the Miller’s Daughter unless mentioned in passing.
I think it would feature in Belle’s story and he probably figured the beast was his father.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass