[SPOILER] Alexander von Brennenburg...

[Googolplex]

...was the grand-uncle of Mandus.

That's what I red in some notes. Does anyone of you already realize that?

[cantremember]

Rich family. he has his big mansion with huge machines underneath and his grand-uncle has a castle.

[Draug]

...and his grand uncle is

Spoiler below!

not a human being.

[Paddy™]

Not to be a Nazi mod or anything, but I distinctly remember this point being discussed in the Plot Discussion thread.

I edited the thread title because you had a rather large spoiler in it, hope you don't mind Googol

[Diz]

...and his grand uncle is

Spoiler below!

not a human being.

This. Or most likely this, anyway. If so, how is it possible that Alexander is in relation with him? And let's say that Alexander was human, why would he have a child? He keeps talking about our world as if it is a horrible and alien place, and he really badly wants to return to this other world. Why would he then consider having or adopting a child for raise in our world?

Interesting topic, by the way! Had me thinking for a bit, actually.

[cantremember]

Wait, so someone impregnated Alexander's sister, or his brother had sex with a human being?

[Alardem]

The other options are Daniel and Herbert, who were both British archaeologists involved with Alexander. Mandus' references to his great-uncle talks about his archaeological findings and 'experiments' in Brennenburg.

Alexander also liked to pass himself off as multiple descendants, so perhaps he'd also have claimed ancestry from numerous families. Maybe Mandus' family was just one of them.

[aquilantiqua]

I'm continually baffled that people don't consider that to be someone's grand uncle (or just uncle) you don't have to be blood related. So say your mother has a sister, and that sister is married to a man. That man is your uncle, but you're not blood related to him right? They don't even have to have children at all, and they're still your aunt and uncle. That man could be an alien insectoid from Neptune, but that doesn't make you part alien insectoid.

So the grand uncle of Mandus could very much be Alexander without him being a partly other-dimensional being, if he just married a German noble woman to keep up appearances while he was masquerading as a baron, and a sibling of that woman is the grandparent of Mandus. Mandus has two coats of arms in his mansion that have heraldic eagles similar to those used in Germany for a long time (as opposed to coats of arms used in England which do not resemble that).

Also Alexander was a founding member of the Order of the Black Eagle and seemingly knew all the Prussian noble families pretty well and they knew him. In general, noble families from an area are all related in some fashion and people, seeing as they thought Alexander was part of the noble line, could have considered him "Uncle Alexander" regardless of just how he was related to them. (Edit: yeah what Alardem said.)

[Diz]

Of course I considered that, but I shrugged it off quickly because it just did not feel all that likely to me. At least, the Alexander we knew from The Dark Descent. He also writes something about distancing himself quite a lot when attending the Order of the Black Eagle in order not to raise further suspicion, since he felt they caught onto him not being human or belonging there (from what I remember anyway), so him being affiliated in any such way was not my first thought. Though now that you mention it, it makes more sense.

[cantremember]

Maybe the term is different in my country, but I've always known an uncle to be a sibling of either of your parents.
An aunt's spouse is, at least for me, not an uncle.

And I think it's more likely the reference is to Daniel, as he is the one who made the archeological finding of an orb, whilst I think Alexander's orb, I don't remember where he got his actually.