[Lordarminius]

I assume he may have died later in life, maybe late childhood

[pvitz]

Spoiler: The real one was adopted and met Johanna later. Source: The story can be found on Kindle Singles, but the BBC article contains basically everything interesting already.

[sulam]

So why weren't there two of them? Or were there and it never became an issue?

[pvitz]

The real one got adopted when he was four years old and his new parents "raised him as their own." He found out about the adoption a long time later. Therefore, it is safe to assume that he also had a different name.