A cover displaying a US 1847 5c red brown pair on an 1851 Canadian cover led a sale of rare stamps at Robert A Siegel in New York on December 15.
The piece realised $55,000, an increase of 83.3% on a $30,000 estimate.
A postal treaty introduced between the US and Canada in April 1851 allowed pre-paid Canadian stamps to be accepted in America and led to the introduction of the 3c Beaver - the first Canadian stamp.
The present lot was sent out in May 1851 and is one of the latest known Canadian covers to display US stamps.
The auction house explains: "This is the finest cover showing use of the 5-cent 1847 issue to pay all of the Canadian postage during the treaty period, which commenced on April 6, 1851.
"Any cover with the 1847 issue used from Canada is rare, but covers mailed during the treaty period with the stamps cancelled by the Canadian target are the rarest and most desirable of all.
"This magnificent cover was featured in the 1956 Caspary and 1957 Dick sales, and, since the European connoisseur acquired it 58 years ago for his collection, it has been unavailable to the philatelic market."
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