The Duchess of Sussex carries her baby girl in one of the illustrations in the picture book.
Archie and Lilibet are likely going to become childhood friends with the children of James Corden and Serena Williams.
Some members of the royal family also agreed that the Queen Mother was "meddling in things she didn't understand."
The Duke and Duchess of Sussex are parents to two-year-old son Archie Harrison and baby girl Lilibet "Lili" Diana.
Royal experts are confident that it was Harry and Meghan themselves who made the purchase.
The Duke and Duchess of Sussex named their baby girl Lilibet "Lili" Diana Mountbatten-Windsor.
The Duke of Sussex is due to attend the unveiling of his mother Princess Diana's statue at Kensington Palace on July 1.
The royals' congratulatory message gave a possible hint about Prince Harry and Meghan Markle's royal titles.
The couple had to attend a photocall with their son Archie just two days after the birth, as is traditional for senior royals.
Buckingham Palace wants Prince William and Kate Middleton to be seen as residents of Scotland rather than visitors.
The Duke and Duchess of Sussex welcomed their daughter on June 4 at Santa Barbara Cottage Hospital in California.
The statue is William and Harry's only remaining joint project since Harry quit as a senior royal in March last year.
Meghan's estranged father Thomas Markle, who also found out about the news with the rest of the world, has congratulated the Sussexes.
A royal expert wondered why the Sussexes didn't choose Diana as the first name for their baby
Princess Anne looked as if she wanted to "exclude" the Duchess of Cornwall by establishing a "barrier" between them.
The Prince of Wales walked Meghan down the aisle at her wedding to his son in May 2018.
With the meeting, Joe Biden will become the 13th American president to meet the Queen.
The family conflict also had an "unexpected consequence" on Kate's marriage with Prince William.
Harry and Meghan want to return to the UK next year for the 4-day celebration marking the Queen's 70 years on the throne.
The family might fly home for Queen Elizabeth II's Platinum Jubilee celebrations.
The 95-year-old and other working royals will soon embark on a year-long nationwide tour to mark the occasion.
The royal household reportedly prohibits "coloured foreigners" from working in clerical roles, only as domestic servants.