Actually, the two men did meet once under unusual circumstances.

This is a most unusual circumstance and might lead to anything.

Except in the most unusual circumstances, we need never think of them again.

Those are unusual circumstances and most people figure they will never have to pay that much.

A married couple find their way back to each other under unusual circumstances.

He is best known for the unusual circumstances of his death.

He still believed that they could, though, especially given their unusual personal circumstances.

Result change: This event is used only under unusual circumstances.

However, there now are certain unusual circumstances in this case.

Obama did not win by that much and in very unusual circumstances.