Credit: GSI Media; Jason Merritt/Getty Images

This means war, indeed!

Before she set her sights on Ben Flajnik, current Bachelor bad girl Courtney Robertson dated more than one Hollywood hunk: former Desperate Housewives star Jesse Metcalfe, Adrian Grenier…and Reese Witherspoon's husband, Jim Toth!

Even Witherspoon, 36, didn't know about her man's long-ago dalliance with the catty reality star, 28 -- first learning the news Feb. 1 upon returning from a trip to Europe.

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But it was no big whup to the Oscar winner. "It didn't faze Reese," a source tells the new Us Weekly of the star, who wed the CAA agent, 41, nearly a year ago.

"There's no way Jim was serious about Courtney," the source sniffs of the model. "How do you go from that chick to Reese?"