Christie Brinkley -- Hottest Tax Debtor Ever

Timeless beauty means nothing to Uncle Sam ... he's slapped Christie Brinkley with a tax lien for over half a million dollars!

Brinkley -- who's worth a frickin' fortune thanks to modeling, infomercials, endorsements and real estate -- was hit with a tax bill by the IRS to the tune of $531,720 ... filed in Suffolk County, NY back on November 21, says the Detroit News.

Guess she's been living in her uptown world a little too long.

3:00 PM PT: A rep says Christie was surprised by news of the tax lien -- and added Christie told her financial team to "resolve the matter immediately."