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Crab has never addressed it specifically in the manga, but come on; with some women you can just tell.
>Righteous and moral to a fault
>Unyielding loyalty
>Fair-skinned, blonde-haired, blue-eyed woman of obvious European descent
>A skilled knight, dedicated to honor and pride
>Zealous about eradicating sources of evil and protecting the innocent
>Strongly opposed to all that which is lewd, despite being a beautiful woman herself
It's the only logical assumption.