A fine pair of 1840 Penny Blacks - aka the world's first-ever postage stamp - emerged as the top lot at Spink's April 14 stamp sale, selling for £85,000.
Elsewhere in the same auction, a single Penny Black commanded just over half that price, affixed to a manuscript dated the first day of issue "London 6 May 1840" and posted from London to Paisley.
The stamp, BF (marking its position on its original printed stamp sheet) is cancelled with two clear strikes of the red Maltese Cross.
The manuscript's date confirms that the stamp was cancelled on its first day of issue - May 6, 1840, was the day the 1d. black stamp, or Penny Black, first entered circulation. It remained in use for a little over a year.
Approximately 78 Penny Black first day covers are known to exist.
Even more impressive is this covers provenance, having once been in the collection of William H Gross, the "Bond King" himself.
Although priced in Stanley Gibbon's catalogue at £125,000, Spink estimated the cover at £35,000-40,000.
The Penny Black official first day cover, sold for £44,000
The extremely rare and highly sought after cover realised a final hammer price of £44,000.
Bill Gross, the American businessman and financial guru, remains the world's most high-profile philatelist - whose status is matched by his dedication to his hobby.
In 2005, Gross paid an incredible $2.7m for a plate block of four 1918 Inverted Jenny stamps.
Then, much like schoolchildren exchange baseball cards, Gross 'swapped' his Jenny Invert Plate-Number Block for a one cent "Z" Grill owned by Donald Sundman.
Today regarded as the 'philatelic swap of the century,' both pieces were exclusively exhibited at last year's MonacoPhil 2009.
Elsewhere, a "cousin" of the Penny Black, the Penny Orange which was issued in Mauritius in 1847, was previously sold by the legendary Philatelist Hiroyuki Kanai in 1993 for over $1m.
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