Okay, so Bob owns a house. Bob marries Jane in an ill-advised, quickly ignored ceremony, but never gets formally divorced. Bob sells his house (in a community property state) to Ted. Ted lives in the house for 20 years. Jane dies. Jane's son Rick goes through her stuff, realizes that she was still married to Bob, realizes that Jane had a legitimate claim on the house that Ted has been living in for 20 years.
This is a classic adverse possession situation. Ted has been openly and notoriously living in this house, acting as owner. If Rick presses his claim, it is likely that Ted can win an adverse possession claim (assuming that Ted lives in a place where adverse possession still works the way it basically did in common law).
I am not a lawyer, this is not legal advice.