Legend in family..Jewish Rabbi married a Polish Countess. had to be the 1800's.
A lovely story. If you have any birth certificates, death certificates etc from the twentieth century, you might contact the Gmina Zydowska in Warsaw who help people to trace their family history.
Often families develop very romantic stories that become more and more romanticised in the retelling however are based on a (sometimes more prosaic) grain of truth. It would be wonderful if you could get to the bottom of the story.