A cover displaying an 1851 Hawaiian 5c blue is valued at $150,000-200,000 ahead of a sale at Robert A Siegel in New York on May 29.
It will lead a selection of Hawaiian stamps from the collection of American financier Bill Gross.
Gross has the largest and most valuable US stamp collection in the world and sales of items from his archive are always hotly anticipated.
The lot is the best of the 10 known surviving covers and features an exceptionally clear and well struck specimen of this rare issue.
It left Honolulu aboard the Zoe, an American brig, on October 22, 1853 and reached San Francisco on November 9.
The journey is documented by the two clear circular date stamps that appear on the front.
Robert A Siegel comments: "For the collector who wishes to have a sound 5c Missionary stamp tied on cover, this is the sole cover meeting that criteria…
"[It's] truly one of the outstanding covers of worldwide classic philately."
Also known as the Missionary issue, the Hawaiian blue is one of the rarest and most sought after stamps in the hobby.
The first white people to arrive on the islands tended to be missionaries and used the stamps to keep in contact with those back home: hence the nickname.
A cover displaying the 13c Hawaiian blue will also be offered, with an estimate of $100,000-150,000.
It's one of the nine recorded covers to display this value and is a supremely attractive specimen.
The record for this issue stands at $2.2m, set for the Dawson Cover (the only example to feature a 2c Hawaiian blue) in 2013.
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