The story
From 24 + Sussex Drive. Until about 1958, 24 Sussex Street (see also drive). The street address of the Canadian prime minister's official residence, since 1951, although since 2015 prime ministers have not lived there because of poor condition needing repair. The road was named in the early 19th century, after Prince Augustus Frederick, Duke of Sussex (1773–1843).
Etymology from Wiktionary, CC BY-SA 4.0.