It's hard to believe, but A.C. Slater is the big 4-0!

That's right -- Mario Lopez celebrates his milestone birthday today.

If you ask us, the "Saved By the Bell" star is looking better than ever. He's still got those incredible dimples and a ridiculously buff body (case and point, this and this).

He's also arguably the most successful of all the Bayside High alum. He hosts "Extra," "The X Factor," "America's Best Dance Crew" and his own radio show ... take that, Ryan Seacrest!

He's also competed on "Dancing With the Stars," appeared on Broadway, has an underwear line, and written both fitness and children's books.

On top of that, he's a father. Mario and wife Courtney Mazza have a daughter Gia, and just welcomed a son Dominic last month!

He's not the only "Saved By the Bell" star who just had a son. Find out who in the gallery above, and see what the rest of the cast looks like now!

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