Robert Frank | @robtfrank

@ CNBC.com

Mobile.de

A replica 1962 Ferrari 250 GTO is on the market for $63 million.

A 1962 Ferrari GTO being offered for $63 million on a German website is being called a contender for the world's most expensive car by some But it's likely the world's most expensive fake.

News outlets have gone crazy for the 1962 Ferrari 250 GTO that's for sale on mobile.de, which is like Germany's eBay for used cars. A story picked up by Fox News said the car "is one of the first of the 39 250 GTOs to have left Ferrari's factory."
Read MoreFerrari GTO may become most expensive ever auctioned
GTOs have sold in private sales for more than $50 million. But the world's leading Ferrari historian and collectible-Ferrari expert Marcel Massini said the car offered on mobile.de is a replica. He has photos and detailed histories of each of the real 39 250 GTOs that Ferrari made, and he knows where all of them are parked.
This car, he said, is not one of them.

"It's a replica," Massini said. "I can tell you that with 100 percent certainty. I know where all of these cars are today. And this is not one of the original GTOs."
He added that the fact that $63 million is being offered on a German used-car website is another clue that the car is a fake.
Mobile.de didn't immediately respond to an emailed request for comment.

But if you're a billionaire GTO buyer, don't be too disappointed. A real 250 GTO is coming up for auction by Bonhams on Aug. 14 in Pebble Beach, California. The estimated sale price: more than $30 million.