With huge billboards in New York City and Los Angeles immortalizing his athletic physique, perfect pecs and artfully tousled beach-blond hair, the formerly unknown Travis is on the fast track to fame now!

As the face -- and figure -- of the new Calvin Klein Body for men line of cotton briefs, Travis follows in the footsteps of such now-famous undie alums as MARK WAHLBERG. In fact, the surfer-turned-model's first in-store appearance at Macy's in Manhattan caused quite a commotion, with crowds of men and women lining up to get Travis' autograph!

"It's flattering but I [don't think] I'm famous," the "it" boy told ET. "It's very weird and a little embarrassing...Modeling, you can't take it seriously. I just do the work and go home."

Travis' mellow mindset is what impressed Calvin when the famed designer met him! The sports and motorcycling enthusiast grew up simply on a farm in the Australian countryside and left home at 19 to explore the world. Eventually, he landed in L.A.

Having gotten into an expensive motorcycle accident just before his departure, a near-penniless Travis showed up at an L.A. modeling agency without a portfolio, shoes or clothes. Undeterred, the agency helped Travis get situated and sent his photo to Calvin and company!

Travis initially didn't want to do underwear ads, but a meeting with Klein himself -- whom the model praises as "down-to-earth" -- convinced the hunk to go for it.

The dressed-down Travis -- found in faded jeans and no shoes on the average day -- says the ads are "about men being comfortable and normal and not pretty-boy." But DANIEL PERES, editor-in-chief of the men's magazine Details, notes that not every man rolls out of bed looking like this male model!

With the ad, "[Calvin Klein] is making life miserable for the average guy," Peres jokes. "I was in a taxi with my girlfriend and we drove by [Travis'] billboard and my girlfriend pushed her face against the glass and went, 'Oh my God!' It makes the average guy feel pretty insecure. This [Travis] has raised the bar to a whole new level. [He's] a tough act to follow."

Travis himself doesn't worry about what it all means. "The food's good...and money's all right," he concludes about his new gig. "I just hope I have as much success as past CK models."

We hope so, too! For more on the adorable Travis, check out ET tonight!