The duke infamously accused her of adultery, for which she was convicted and beheaded. Most contemporary commentators believed the charges false, or a pretext, and offered other explanations for the duke's accusation.
One explanation is that Beatrice was conspiring against her husband with diplomats* whom the "king of the Romans" Sigmund (most do not call him emperor yet) had sent to Milan in 1418. Although plausible, the earliest suggestion I could find of this explanation was made in 1726, by Claude Fleury in his Histoire Ecclésiastique. He generally cites the continuators of Baronius, and in this paragraph his only reference is to Rinaldi, but the story appears neither in Rinaldi nor in any of the others.
Yesterday however I read the anonymous 1970 biography of "Beatrice, duchessa di Milano" from the Dizionario biografico degli italiani,
https://www.treccani.it/enciclopedia/du ... rafico%29/
This author mentions Eberhard Windeck's (c. 1380-1440) contemporary witness to the story, along with the story of her conspiracy with Sigmund's diplomats (I still do not know how Fleury could have known about it, though).
Altmann's edition of Windeck's chronicle is thankfully available, and in his edition the chapter is XCVI, pp. 94-95.
http://www.rosscaldwell.com/marzianotex ... ewindeck94
I have edited the critical notes so that they only apply to our text, hence the appearance of the page.
http://www.rosscaldwell.com/marzianotex ... ewindeck95
I need help with this German. This question is primarily addressed to Huck, obviously. Can you make at least a rough translation?
Here is Altmann's edition of Windeck at Heidelberg:
https://digi.ub.uni-heidelberg.de/digli ... w_hidden=0
Or scroll to pages 94-95 -
https://digi.ub.uni-heidelberg.de/digli ... 013/scroll
*Fleury calls these diplomats the Bishop of Passau and the Count of Oettingen.
In 1418, the Bishop of Passau was Georg von Hohenlohe (1348 or 1350 - 3 August 1423).
This title was actually "prince-bishop" (Fürstbischof), which combined secular and ecclesiastical rule.
The Count of Oettingen was Ludwig XII of Oettingen (1361- 28 October 1440), named by Windeck in chapter LXXXIV, page 85: "grof Ludwig von Öttingen hofmeister des Romschen konigz."
https://gw.geneanet.org/jksir?lang=en&p ... +oettingen
https://www.genealogieonline.nl/fr/stam ... 505495.php
https://books.google.fr/books?id=05lAAA ... 22&f=false