Not exactly the same, but Oathbreaker is at least one option for the old Blackguard concept, specifically covering the "fallen to dark side" case.

But a LE/NE/CE Paladin with another Oath falls within the Blackguard concept too, and you can start at 1st level. In some cases, it might even work better, for example if you're undercover and your good-looking spells will help you against being busted.

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