This well-dressed pair is the mentally unstable King Imre and his sister (who also becomes his lover) Ariella. They are from Katherine Kurtz' "Camber" series, a parallel storyline taking place about 300 years before her "Kelson" series. In the story, a dynasty of corrupt and crazy Deryni was on the throne of Gwynedd, and Camber, the political hero, warrior, and kingmaker, tries to overthrow them and place another royal heir in power. This takes a lot of books to tell.
This whole image was borrowed from archival photos of a lavishly staged play (or was it a silent movie, I forget) from the early 20th century, when there were no computer-generated effects and you had to build sets and costumes for real. The look of Camber was inspired by the Byzantine era, with of course a lot of Anglo-Celtic influence as well.
Painting is 8" x 10", acrylic on illustration board, February-March 1986.