Complex sentence: The cousin of Ladislaus IV, Andrew III the Venetian was crowned King, despite the desire of the sister of the former King Ladislaus IV, Mary of Hungary, Queen of Naples, who wanted her son, Charles Martel as the new King in Hungary.
Split into simpler sentences: The cousin of Ladislaus IV, Andrew III the Venetian was crowned King. Although, sister of the former King Ladislaus IV, Mary of Hungary, Queen of Naples, wanted her son, Charles Martel as the new King in Hungary.