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Do you remember when these famous co-stars dated?

Sometimes the real excitement starts after the cameras stop rolling!

In Hollywood, it's commonplace to fall in love with a co-star -- and sometimes the love lasts long past the red-carpet premiere. (Power couple Blake Lively and Ryan Reynolds first met on set of 2010's "Green Lantern"!)

But more often, co-star romances are short-lived and, in retrospect, super weird. Check out these celeb pairings you probably forgot about: