Mrsdof
I loved Philippa Gregory, Jean Plaidy and Anya Seton. My all time favourite book is Katherine by Anya Seton. It is the true love story between John of Gaunt and Katherine Swynford. Their great granddaughter, Margaret Beaufort, was the mother of Henry Tudor who became Henry VII. I have read it three times over the years and never tire of it. 
Same here! I absolutely loved Katherine. I was 13 when I read it and still think of it to this day. Just recently, as I do every year around now, I found myself thinking "the tender green time of April" while admiring the beautiful spring foliage and blossom all around.
It could surely have made a wonderful film.
My second favourite Anya Seton is Green Darkness, which is set in the 60s but interweaves the story of a girl who was 'walled up' in the 16th century because she was expecting the child of a monk. The setting for this is Ightham Mote in Kent, which is one of the best preserved medieval manor houses in the country. I've always meant to visit it.