Complex sentence: While in Paris in the 1870s, Mancini met Impressionists Edgar Degas and Edouard Manet, and became friends with John Singer Sargent, who famously pronounced Mancini to be the greatest living painter.
Split into simpler sentences: While in Paris in the 1870s, Mancini met Impressionists Edgar Degas and Edouard Manet. He became friends with John Singer Sargent, who famously pronounced him to be the greatest living painter.