I watched S05E06 and the look of regret, or was it sadness, was obvious in the Countess. I hope that there would be a budding romance between them as she clearly loves him then, and perhaps now? Prince Kuragin said he loved her more than he did his wife.
Both the Countess and the Prince have a lot of on-screen chemistry. It seemed kind of sad to me that she stayed with Lord Grantham for over 50 years? (how old is she really?) just because of the kids and perhaps convention. She said she did not think they were totally unhappy but she probably could have been happier with Kuragin.
Only problem is that his wife is still alive and in Hong Kong. Have to solve that issue first before they can get together. A divorce is unheard of in 1924 I guess, so it either has to be the wife dies, or goes missing in action.
It is also just heart-warming to see a softer romantic side to the Countess, no?