There's only one Difficult Dukes book so far

Thomas Rowlandson, A Book Auction

I've heard from a couple of readers who are wondering whether they missed a book in the new series. It took a little while to figure out what led to this conclusion. Eventually I realized: References are made in A Duke in Shining Armor to the Duke of Blackwood's having married Ripley's sister a year earlier. Since I often refer to past events that are in my head, and will eventually (I hope) be worked out in ensuing books in the series, as part of the series...