There is also an "Avenue De Lafayette" off of Washington St in Downtown Crossing, which at one point in the 90s got a horrible street sign that said "De Lafayette Ave" (now fixed).I live at the intersection of Prince St and Lafayette AVENUE in the North End. My wife and I joke about it all the time, because it's basically an alley. I have to imagine neither the name nor the designation is original.
Seems strange that there are two streets with nearly the same name so close together. Must be an interesting story there.