The 1904 6d Pale Dull Purple (I.R. Official) was sold to an anonymous private buyer by Stanley Gibbons Investment.
The stamp was issued on 14 March 1904, but was withdrawn almost immediately after issue.
Only 19 sheets were ever printed and on withdrawal, almost all were destroyed.
Director of Stanley Gibbons Investment, Keith Heddle, said: “The 6d I.R. Official is one of the most sought-after stamps in the world.
“Understandably our client is thrilled to own such a unique and coveted piece.”