Complex sentence: In Florence he met the Countess of Albany Princess Louise of Stolberg-Gedern, who had been the mistress of Vittorio Alfieri, while in Rome came into relationship with Antonio Canova and the German painter Sophie Reinhard.
Split into simpler sentences: In Florence he met the Countess of Albany Princess Louise of Stolberg-Gedern, who had been the mistress of Vittorio Alfieri. In Rome she came into relationship with Antonio Canova and the German painter Sophie Reinhard.