Marriage finder says "Hon Herman C Von Nieroth married one of these people
Lewis Powell, Herman Carl Von Nieroth, Selina Margaret Hunter, Catherine Evans". And for the other record, "Selina Margaret Hunter, Hon Herman Von Nieroth, Catherine Evans".
I think we can assume it was either Selina Hunter or Cathering Evans.
So did 'the baron' meet Kate Sawtell in Wales, and move to London with her in 1890?