Complex sentence: Like his father, the younger Gilbert was in the service of John Mowbray, 4th Duke of Norfolk, and also obtained a royal office, the Clerk of the Market, in 1461.
Split into simpler sentences: Like his father, the younger Gilbert was in the service of John Mowbray, 4th Duke of Norfolk. He also obtained a royal office, the Clerk of the Market, in 1461.