i know the old kaiser hated nazis (another good indication that they weren't as conservative as everyone paints them to be nowadays), so it's possible even if they wanted him to return he wouldn't. i can't remember the exact quote but i believe he said something about how he wouldn't sit on the throne with a nazi banner above it or something. but even if wilhelm wouldn't return as kaiser, they literally could have just picked somebody. germany at the time was full of uprooted noblemen with lots of claims to lots of thrones. they could have just had an open casting call for anyone with "von" in their last name to show them a forged genealogy giving them a claim to the throne. then stick a crown on his head and make him a puppet figure to appease people
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