Mr Pim by A.A. Milne

Absent-minded Mr. Pim (who is known for confusing names and people) drops in on the Marden home on a business matter one day, and in the way of conversation, announces that Mrs. Marden's first husband, thought to be deceased, is actually alive. Mrs. Marden is, therefore, a bigamist. Since Mr. Marden is very conventional and properly English (and a trifle pompous and tyrannical, to boot), he very upset. But later, Mr. Pim drops by again, and reveals to Mrs. Marden, that by accident, he had confused the two names. No doubt Mrs. Marden's first husband is, indeed, dead. Mrs. Marden uses this information as a tool to get what she wants in her house and also to force Mr. Marden to allow his niece to marry the artist who loves her.

George is a fine upstanding citizen and a stickler for doing the right thing. He has a devoted wife, Olivia, and is guardian to his somewhat flighty niece, Dinah.But his careful peace is broken when Mr Pim casually announces that he's recently seen an ex-convict from Australia, Telworthy.

The only thing is that the character sounds awfully like Olivia's first, and supposedly deceased, husband… and if he's really still alive, then Olivia is a bigamist.