The secret is out - X17 can reveal exclusively where Kim Kardashian will be getting married August 20!

Last month, Kim and fiancé Kris Humphries revealed on their wedding invitation that the black-tie affair will be held in Montecito, Calif. But now we know that it will be at the same $29 million estate where Jennifer Lopez and Ben Affleck were going to be married at back in 2003, before they broke off their engagement!

There is already a ton of prep work being done at Sotto Il Monte, a 10.9-acre mansion owned by a venture capitalist from Northern California.

An X17 photographer on the scene yesterday tells us, "This is gonna be big. The estate is amazing. And security is going to be super tight. There are NO holes in the perimeter of this property - it's already on lock-down."

Kim has been busy prepping for the wedding, squeezing in a last-minute dress fitting in New York City last week plus tons of gym sessions and late-night beauty appointments leading up to Saturday's big event.