Count Micheal Vorontzov was raised to the title of Serene Prince Vorontzov for his part in wars against Napoleon.
Actually, much later: in 1852. So Pushkin's affair was with a countess, not serene princess. It's commonly agreed today that his derogatory remarks (in poetry and in correspondence) about Michael Vorontsov had little to do with the real character of this talented, enlightened and courageous general and statesman.
