The new design for banknotes featuring the face of King Charles III will be unveiled before the new year.
But the public will not be able to get their hands on the cash and use it to pay for bills and shopping until mid-2024.
Coins featuring the new monarch will enter circulation in line with demand from post offices and banks.
These will be used alongside coins featuring Queen Elizabeth II "for many years to come," according to The Royal Mint.
Money depicting the former monarch will be replaced over time as coins and notes become worn or damaged.
Anne Jessopp, CEO at The Royal Mint, said: "We are honoured to have struck each UK coin of Her Late Majesty’s reign, documenting her journey from young Queen to respected Head of State.
"As official coin maker to the UK, we have told the story of each monarch since Alfred the Great and are now preparing for the biggest change in British coinage for several decades.
"The first coins bearing the effigy of His Majesty King Charles III will enter circulation in line with demand from banks and post offices.
"This means the coinage of King Charles III and Queen Elizabeth II will co-circulate in the UK for many years to come."
All UK coins showing the effigy of Queen Elizabeth will remain legal tender and in active circulation for the public to use and spend as normal.
This is to ensure that the changeover of money to the new design goes smoothly with minimal environmental impact and cost.
It is not the first time the nation will have cash featuring two different monarchs at one time, with the process being commonplace for coins.
New banknotes depicting King Charles are expected to be in use by mid-2024 and his portrait will appear on existing designs of the £5, £10, £20 and £50.
The King will's effigy will face to the left while Elizabeth II's effigy faces to the right, as part of a tradition from the 17th century to alternate the way successive monarchs are facing.
No further design changes will be made, the Bank of England confirmed.
Some 27 billion coins are currently circulating in the UK with the portrait of Queen Elizabeth II.
Further details about the coinage of her son King Charles will be unveiled over the coming weeks by The Royal Mint.
Like the UK's current banknotes, those depicting King Charles will be made of polymer which is longer lasting and more difficult to copy.
Former paper banknotes are due to expire in just three days, with Brits being urged to cash in their old £20 and £50 notes.
The Post Office is prepared to handle huge queues, with £14 billion of old paper notes currently still in circulation according to the Bank of England.
Since January, £1.2billion worth of old notes have been deposited at Post Offices across the country.
They will stop being legal tender after Friday when they will become worthless in shops and stores but can be taken to the bank and exchanged for new polymer notes.
Post Office banking director Martin Kearsley reassured that most of Britain's 11,500 branches are open long hours with staff on hand to help with the process.
