I'm looking for a short story I read 2-5 years back. I'm pretty sure it was in a anthology of short stories about magic, possibly about wizards specifically. I believe that the anthology was recent.
In the story, wizards get their magical power from a single secret they keep. The fewer people know the secret, the more powerful their magic is, and if another wizard learns your secret they have power over you. The plot of the story focuses on the protagonist, a very powerful wizard, fending off an attempt from a rival to discover their secret. The plot involved tricking or enchanting a young bar maid (or similar) to become enamored with the wizard.
At the end, the secret is revealed to be
that the wizard is actually a woman.