This is a two-coin Sovereign set representing a new chapter in the British monarchy. The Mint says about it:
"Upon the passing of Queen Elizabeth II, His Majesty The King promised the nation his ‘lifelong service’. King Charles III’s pledge echoes the promise his mother made in her 1957 Christmas broadcast. To honour the legacy of Britain’s longest-serving monarch and The King’s accession, we have curated a two-coin Sovereign set that unites their reigns."
The set has a 1957 sovereign depicting the first definitive coinage portrait of Queen Elizabeth II by Mary Gillick, and a 2022 Memorial Sovereign depicting the First Portrait of King Charles III. The 1957 coin is circulated (in Extremely Fine grade), while the 2022 coin is in Proof FDC grade.