The best thing about going to a high school reunion, is seeing how everyone’s lives -- and looks -- have drastically changed!

When American Pie hit movie theatres in 1999, the cast of young actors was thrust into the public eye becoming international stars overnight.

Who was it that said men age better than women?

One-time A-list heartthrob Val Kilmer looked every bit his 51 years when snapped on the Cincinnati, Ohio set of his film Seven Below, back in August.

Kilmer, who turns 52 New Year's Eve, sported frizzy, straw-like hair and a weathered face and was barely recognizable from his Top Gun Iceman days.

Now that’s what we call a transformation!

Jonathan Lipnicki, who played Renee Zellweger’s adorable bespectacled son in the blockbuster flick Jerry Maguire, is all grown up and recently revealed his new and improved, shockingly buff body – and RadarOnline.com has the unbelievable photo.

The 21-year-old, who also starred in Stuart Little and Like Mike, has been training in mixed martial arts – and all the hard work has definitely paid off.

Nothing Compares 2 a shocking celebrity transformation!

Sinead O'Connor, who skyrocketed to fame in the early 1990's with her timeless tune Nothing Compares 2 U, hit the stage at a music festival in Ireland over the weekend, looking almost unrecognizable - and RadarOnline.com has the photos.

PHOTOS: Sinead O'Connor's Shocking New Look

The 44-year-old flaunted a much fuller figure, wearing a crop top over a mesh shirt with a black blazer and ill-fitting trousers, as she performed back-up vocals for Natty Wailer at The Bray Seaside festival.