One of the world's greatest living scientists, Dr Watson won the award for his ground-breaking discovery in 1953, alongside Dr Francis Crick and Maurice Wilkins, of the structure of DNA: the double helix.
A Nobel Prize medal had never before been offered for sale by a living recipient.
The medal was estimated at $2.5-$3.5m with Dr Watson planning to use a portion of the proceeds to continue his philanthropic legacy.
The sale took place on December 4 and the buyer's premium was 25/20/12%.
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