Prince George’s first birthday on July 22 will be marked with a commemorative STG5 coin.

Prince William and Kate’s son is the first member of the royal family to have his first birthday honoured with a new British coin.

William and Kate, along with George’s great-grandmother the Queen and Chancellor George Osborne approved the design of the sterling silver piece, which bears the heraldic royal arms and the year 2014.

Shane Bissett, director of commemorative coin and bullion at the Royal Mint has confirmed the occasion would be marked by the commemorative coin.

“As Prince George of Cambridge reaches the significant milestone of turning one-year-old, we felt there could be no more fitting design to mark the first birthday of our future king than the royal arms – the arms of the monarch – minted in honour of the future heir to the throne.

“The choice of a silver coin is significant too as the precious metal is closely associated with newborn babies, as crossing the palm of a newborn baby with silver is a way to wish them wealth and good health throughout their life, whilst the STG5 coin is a favourite for royal celebrations.”

There will be a limited mintage of 7,500 of the birthday coins, which will cost STG80 ($A146) each.

Both George’s birth and his christening were marked with commemorative coins. The STG5 birthday coin will be available via www.royalmint.com.