EXCLUSIVE

Queen Elizabeth's dirty, old undies will have a new home ... after a mystery panty raider snatched 'em up at an Internet auction for $18k.

The knickers had been placed on eBay by the estate of the late "Baron" Joseph de Bicske Dobronyi ... who had claimed he came into possession of the undergarments after they were left on a private plane when the Queen visited Chile in 1968.

But after a cyber auction consisting of 18 total bids, one lucky mystery buyer emerged victorious. So far, his identity has not been revealed ... and we're guessing it probably won't be.