I have a married couple in my tree (who admittedly were childless) where the wife's death was informed by her great-nephew-in law (my direct ancestor, grandson of her husband's sister) and the husband was informed by a great nephew from an entirely different branch of his family, the descendant of his brother, whose birth I didn't even know about and traced subsequently. I've also had sons-in-law informing on deaths or even, in one confusing occasion, a step-son when we had no idea he had remarried slightly prior to death. It is most likely to be a spouse or child to inform, however, but if you are stuck it might be worth a chance.
What about checking newspapers? If there was a death notice, it might say where he was formerly native of. Have you checked the original parish records for his marriage? It might also give an indication of where he came from, although that might not necessarily be where he was born.
One other thing I might suggest is researching this other person to see if you can find traces to indicate there was another person. If they were separate, you might find a marriage or death that isn't yours, for example. You might find evidence through lack of evidence, if you see what I mean.
