irishpapermoney.com

I came across this recently.
From Spink Auction: 1023 - World Banknotes 
Lot: 253.

From the catalogue description:
Colonial Bank, $5, Saint Thomas, 1 January 1879, ´Issued at St. Croix branch´ top left and right (Pick unrecorded), a fresh white and attractive example, very fine and of the highest rarity, possibly a discovery note, a truly special note.
Estimate £5,000-7,000.

It sold for £25,000, plus fees.
.
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Interestingly, St Thomas, and St. Croix were both part of the Danish West Indies at the time.

Some background information on the operations of the Colonial Bank on these islands is mentioned on an article about the
The Danish-West Indian National Bank.

The Colonial Bank commenced business on 15 May 1837 in Trinidad, Jamaica, Barbados, British Guiana, and St. Thomas. It was an initiative by London bankers and merchants to create a banking system in the West Indies.

The Colonial Bank Correspondence 1837 - 1885 archive of early correspondence provides some useful background information on the bank, which was a forerunner of Barclay's Bank.

Here is an Ulster Bank 30 shillings note from the 1830’s which is similar in design to the Colonial Bank $5 !

Interesting indeed!
Not a unique occurrence.

I do recall that Colonial Bank 5 Dollar turning up at the time. A very nice find.
And that Ulster Bank 30s does share quite a few of the design features.