Saw this book review and thought it sounds very interesting:
http://www.thedailybeast.com/articles/2013/05/12/world-war-ii-s-strangest-battle-when-americans-and-germans-fought-together.html?

But is it really as true as they say?

Funny part is where initially it talks about the wives & mistresses of the French VIPs joining the fight it kind of implies the French men didn't....it does clear that up later in the review but the the end of the first paragraph in the review is funny.

Sounds like an interesting idea, for a diorama. I'll have to buy a copy.

It would appear that the author, Andrew Roberts has had a somewhat checkered career, some of his works are highly regarded, others considered revisionist. I would like to see what sources he used for this story and frankly would like to see other mentions of it before I accepted it as true.

Google search for "wwii Schloss Itter battle". Several results, although many are about the book.