'Cruel Intentions' Co-Stars Sarah Michelle Gellar and Reese Witherspoon's Sons Are Besties!

This video is unavailable because we were unable to load a message from our sponsors.

If you are using ad-blocking software, please disable it and reload the page.

The friendship forged between Sarah Michelle Gellar and Reese Witherspoon lasted far beyond their time on the set of Cruel Intentions!

Speaking to ET on Wednesday, Sarah revealed that she and Reese have remained close, especially since their kids have become besties.

WATCH: Reese Witherspoon, Sarah Michelle Gellar and Selma Blair Have Amazing Cruel Intentions Reunion!

"Reese's son and my son are best friends," Sarah shared, adding that, sometimes, they even carpool together.

It's because of this closeness that a recent on-stage musical revival of Sarah and Reese's 1999 teen drama came as such a surprise to the stars, for a number of different reasons.

"We all see each other, so you don't realize you're getting older," the 38-year-old actress said. "Then all of the sudden you're faced with the revival of your movie, with all these young kids in it, and were like, 'Oh, we're old.' That's when it hits you."

WATCH: Sarah Michelle Gellar Shares Super Cute Pics of Her Kids in the Kitchen!

Check out the video above to hear more from Sarah about her family, and how they inspired her to launch the culinary lifestyle brand, Foodstirs!

Also, here's a look at Sarah and Reese's recent reunion with their Cruel Intentions co-star Selma Blair: