Beata Christiernin - Regarding the suggested affair with the king Fredrik I

The memoirs of Admiral Carl Tersmeden which you have identified appear to be the most detailed account of Fredrik I's relationship with my 4x great grandmother - and it is certainly that Beata as her sister, married to a Stockholm priest, is also mentioned. We don't know how long the affair lasted, but there were at least two other short-term mistresses before Ebba Horn was appointed as the official 'maitresse'. That she was already married and had children probably didn't matter to the king as long as she had 'a well turned leg' - married royal mistresses were often favoured as there was less risk of a resultant child making a claim on the throne. It was not, by the way, the castle Beata moved into, but the house on Riddarholmen where her predecessor Hedvig Taube had lived. Tersmeden was clearly not proud of his part in 'procuring' Beata for the King - not least, perhaps, because she was his 2nd cousin once removed.

Thanks for the info and analysis which I think makes sense! Here are some other sources of interest on the issue:

http://historiska-personer.nu/min-s/p9afef55c.html
https://sv.wikipedia.org/wiki/Hedvig_Taube