There's a saying, "once in a life-time event," and that's just what this is.

He resolved to embark on a once-in-a-lifetime enterprise.

A hundred years is called a century.

About the wedding ... It's a once-in-a-lifetime chance to be the main attraction so instead of doing it on a shoestring why not pull out all the stops and make a great show of it?

Only after a century and a half of confusion was the royal authority restored.