I just had a strange flashback to a conversation I had when I was in high school, with a man who was regarded by many members of a particular online community as having an impressive degree of knowledge of the English language.
The conversation centered on a claim this man made that I found very difficult to accept. I had made some remark involving the difference between it's and its (a distinction which I trust is quite well-known to the majority of users on this site), to which he had contributed, mostly phrased as an amusing aside, that there was one more word I hadn't mentioned: its', with the apostrophe at the end.
I originally thought he might have been joking, but we ended up debating this rather fervently. I seem to recall that I kept demanding he use the word in an example sentence, but he either could not or refused to do so. Yet he maintained that it is a word.
Is this true? I must concede I haven't put a lot of thought into it just now; but at the time, I was perplexed by the very suggestion that it could be a word (what could it mean?), and at the moment I can't really think of any scenario where it would make any sense.