A guest on the Antiques Roadshow has been left floored - quite literally - after learning the true value of a Rolex watch he bought back in 1974 for $345.97.

The man, identified only as David, visited appraiser Peter Planes during the filming of the show in West Fargo, North Dakota. David revealed he had bought the Oyster Cosmograph back in 1974 while serving with the Air Force in Thailand, thinking it would be useful to use while scuba diving.

You can see the remarkable evaluation below:

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Clearly excited by the rare timepiece, Planes told David that the watch was very similar to the one worn by late actor Paul Newman (Cool Hand Luke) that auctions for around $200,000 - but this only garnered a nod from the owner.

Planes then informed David that watches that are inscribed with the word 'Oyster' are considerably rare due to the short manufacturing time, and that watches like David's were worth more in the region of $400,000.

After hearing the monumental figure, David that performed what appeared to be a pratfall to the floor - leading to Planes asking if the owner was okay. Incredibly, Planes wasn't finished, because he had yet another revelation for David.

Once David had jumped back up, Planes said: "Don't fall. I'm not done yet", before going on to explain that watches LIKE David's sold for that high.

Related - This man had a similar reaction when he learned the true value of his watch:

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Planes then explained that due to the near-perfect condition of David's watch, and the fact it was accompanied by all the relevant documentation, the true value of the timepiece is more in the region of "$500,000 to $700,000".

Speaking to The Washington Post, Planes later revealed that the value of the watch would be "life-changing for somebody".

But David never revealed whether or not he would be selling the watch, as Planes explained: "He’s saved it all these years. He may be saving it more."

'Antiques Roadshow' guest is literally floored by value of Rolex watch he paid $346 for