Viv was Cleopatra in 1945. Cesar and Cleopatra was an Alexander Korda production if I remember correctly.
Claude Raines was Cesar and Flora Robson was Ftatoteeta.
Cesar and Cleopatra was based on the George Bernard Shaw play. As I remember it when Vivien asked G B Shaw if he thought her a good enough actress to play Cleo, he replied that she shouldn't be silly. The role plays itself.
" ...the happiness in the tune convinces me that I'm not afraid."