Complex sentence: John Mowbray, 4th Duke of Norfolk (1444--1476) was the only son of John de Mowbray, 3rd Duke of Norfolk and Eleanor Bourchier.
Split into simpler sentences: John Mowbray, 4th Duke of Norfolk was born in 1444 and died in 1476. He was the only son of John de Mowbray, 3rd Duke of Norfolk and Eleanor Bourchier.