EXCLUSIVE: Rande Gerber and George Clooney: Secrets behind Hollywood's ultimate bromance

ET visited Cindy Crawford's husband, Rande Gerber, at his office in Malibu, California, and got the story behind the couple's close friendship with George Clooney and wife Amal.

At the crux of this relationship is Gerber's bond with Clooney, which started before either of the men were married to their current wives.

WATCH: George Clooney Was 'Forced' Into Starting Tequila Company

"George and I met probably over 20 years ago," Gerber shared with ET. "He was shooting a movie in New York. I owned a bar at the time and he was coming in and we just became friends. We'd have a couple of drinks, couple of tequilas. Actually we met over tequila."

See images of George Clooney:

Meeting over tequila is meaningful, as they now own their own tequila company -- Casamigos. The drink debuted on the U.S. market in 2013, but started out as a private passion project between Clooney and Gerber. The two friends were on a mission to create the perfect tequila -- and after two years developing it and then two additional years drinking it, they were informed they had been ordering 1,000 bottles of Casamigos a year.

According to Gerber, he and Clooney were told they had to get licensed and "get legit" in order to keep producing the tequila.

WATCH: George Clooney Takes Amal Home to Kentucky, Hangs With the Locals

"They said... either you're selling it or you're drinking too much," Gerber explained.

Turning their passion into a business hasn't diminished their love of the product they created, and in fact helps them in the decision-making process.

"If we find that we're disagreeing on something, we'll usually have a drink," Gerber said, "and another and another and at the end, we've agreed somehow."

Casamigos (loosely translated "House of Friends") is named after the property in Mexico that Gerber and Clooney share.

Clooney is frequently snapped rocking the brand's logo; Cindy and Amal are also fans.

"He's giving it as gifts and he's bringing it to restaurants just in case they might not have it," Gerber said.

WATCH: George Clooney Photobombs Cindy Crawford and Rande Gerber in Ibiza

ET has a glimpse into their friendship and lifestyle away from the glamour of Hollywood through never-before-seen footage of Clooney and Gerber on their trip to Jalisco, Mexico last year.

In the clips, it's clear that they're not just friends, but also road trip buddies.

"We just get on the [motorcycles] and we go," Gerber said.

Watch the video above.