1899 Belgium 50 Centimes 1899 Reverse Muled with a 1907 Obverse
NGC MS 63
This is a Belgium 50 Centimes struck during the reign of Leopold II. The reverse die is dated 1899 but was incorrectly muled with an obverse die dated 1907. Obviously this was an intentional muling to create a rarity and fantasy piece. In 1907, the mint used a die for the reverse dated 1899.
This illustrated definition of a mule is from
the glossary section of Mint Error News.
This should have been the correct obverse
using the 1899 die, not the 1907 obverse die:
Below is a fascinating and unique Gold Belgium Franc Obverse Die Trial from the same time period also featuring Leopold II Koning on the obverse: