Born in 1785, William Augustus Montagu was an illegitimate son of John Montagu, 5th Earl of Sandwich, by Maria. He was baptised at St Anne's Church, Soho, Westminster. William is thought to be named after his uncle, William Augustus, who died at Lisbon in 1776. His grandfather was John Montagu, 4th Earl of Sandwich, who served three non-consecutive terms as the First Lord of the Admiralty, to 1783.
