You can go to a thousand concerts and see what’s printed on the ticket – the headliner plus a support act – and nothing more.

But then there are those magical moments when the featured act invites a friend or two onstage, resulting in one of those legendary surprise appearances most people only read about.

How about it? Have you ever witnessed a surprise walk-on? Were you in the audience when Springsteen brought out Jackson Browne, when Mary J. Blige dropped in on Jay-Z or Paul McCartney joined Billy Joel?

Surprise guest appearances at concerts is this today’s Friday Fun topic. It’s time to share those astonishing moments by letting your memories flow into the comment thread below.