Officials at California State Prison, Corcoran tell us the visit occurred on Sunday morning -- the day before V-Day -- because no visitors are allowed during the week.
We're told Manson is "very choosy" about who he meets with -- and rarely accepts visits -- but for some reason, he gave the green light to spend time with a certain lucky lady.
Officials wouldn't reveal the woman's name -- but we're guessing she probably wasn't Jewish ...