Complex sentence: Two years later he married, in London, Giulia Grisi, a star soprano with links to the patrician Colonna family and thus the Royal Houses of Greece and Russia.
Split into simpler sentences: Two years later he married, in London, the leading soprano Giulia Grisi, also of noble extranction. Grisi had links to the patrician Colonna family and thus to the royal houses of Greece and Russia.