The Fame Bureau is holding an exceptional sale of music memorabilia, We Will WOCU, on May 27 in London.
It was gifted to The King of Rock 'n' Roll by Barron Hilton, co-chairman of The Hilton Hotel group and grandfather of Paris Hilton, on the closing night of his 1975 tour.
Elvis wore the medallion with his "Rainfall Jumpsuit" (pictured) during the gig, which took place at the Hilton hotel in Las Vegas.
According to the Fame Bureau, the medallion is made of solid gold, surrounding an exceptionally rare 1924 St Gaudens $20 gold coin.
For the uninitiated, the St Gaudens double eagle coin is among the most collectible in the world. (You can read more on the Story of the US double eagle coin here).
Within the gold, there are 40 round cut diamonds, each measuring 1.6mm in diameter with colour H, clarity VS2.
The medallion also contains an additional 12 round cut brilliant diamonds measuring 3.45mm colour H clarity VS2.
In total, the diamonds weigh 2.60 ct, while the gold weighs 870 grams on the end of a 30 inches-long 18kt fox-tail design chain.
To verify this medallion's incredible and singular provenance, it will sell with jewellers' appraisals and a history of its origins and owners from Elvis Presley to the present day.
Elvis's medallion contains a highly rare and collectible 1924 St Gaudens
It will appear for sale with an estimate of £725,000-£1m. Bids will open at a staggering £360,000, with live bidding available for collectors outside the UK.
The sale will be unmissable for collectors and investors in Elvis and music memorabilia, and of great interest to numismatists (it's certainly among the most unusual sales on this year's coin collectors' calendar).
Other exceptional memorabilia items in the Fame Bureau's sale include Elvis's 1957 Black and Pink Cadillac (£175,000-£200,000) and a stunning Peace Campaign Banner entitled WWIII by John Lennon (£25,000-£30,000).
In other Elvis memorabilia news, two excellent photographs of The King at his peak, one smiling, one brooding, each with clear signatures in blue ink are currently available. There is also a Las Vegas menu signed by Elvis (along with Vernon and Dee Presley, Colonel Tom Parker and Charlie Hodge).
And if you're a collector on the lookout for exceptional John Lennon memorabilia, a couple of amazing pencil sketches executed by John Lennon during his first year at Liverpool Art School are also for sale.