When 13 Going on 30 premiered in 2004, it made hearts swoon! The quintessential romantic comedy starred Mark Ruffalo and Jennifer Garner, but there were a few other now-famous faces in the film. It took 15 years for Mark to find out that his Avengers: Endgame costar Brie Larson also starred in the movie! Scroll through to see Mark’s reaction and to learn which other child stars made their big-screen debuts in the flick!


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