Great Britain. 500 Pounds, 2015. KM-unlisted. Silver Kilo, 32.15 ounces. Struck to celebrate Queen Elizabeth II becoming the longest reigning monarch in British history. Authorized mintage of 320. This example one of the first 100 struck. Portraits of the queen spanning the length of her reign. Originally sold by the British Royal Mint for £2,000.00. NGC graded Proof 70 Ultra Cameo. Estimate Value $1,500 - 2,000