However, brand and reputation management expert Eric Schiffer believes this reported sum is wide of the mark.
He told Express.co.uk: “It doesn’t comport with modern publishing economics, it’s just not real.
“The numbers are likely large but nowhere near that.”
Prince Harry is writing a memoir
Prince Harry and Meghan live in California
While he believes it unlikely the Duke of Sussex was handed a $20m cheque, Mr Schiffer believes Harry’s book will receive a lot of attention from the public.
He said: “This $20m sum is just too high, but I think the book will get wide attention in light of the timing.
“Also, it will get attention due to the speculation about what’s inside and whether it will have more reveals about Prince Charles and perhaps about how Meghan and Harry were treated at the Palace.”
Mr Schiffer also believes there is a chance Harry could use this book to narrow the gap created by the rift with the Royal Family.
Prince Harry’s memoir will cover his life from his childhood to fatherhood
Upon announcing the book deal, neither Harry nor Random House mentioned the size of the deal.
But they stated the Duke of Sussex will donate proceeds to charity.
Express.co.uk has contacted Random House for comment.
Prince Harry and Meghan spoke to Oprah Winfrey earlier this year
Prince Harry’s memoir is due to be released in late 2022
A statement published on Archewell.com said the book “will share the definitive account of the experiences, adventures, losses, and life lessons that have helped shape” Harry.
Speaking about his work-in-progress, the Duke said: “I’m writing this not as the prince I was born but as the man I have become.
“I’ve worn many hats over the years, both literally and figuratively, and my hope is that in telling my story — the highs and lows, the mistakes, the lessons learned — I can help show that no matter where we come from, we have more in common than we think.
“I’m deeply grateful for the opportunity to share what I’ve learned over the course of my life so far and excited for people to read a firsthand account of my life that’s accurate and wholly truthful.”
They have since set up their own organisation, Archewell, which includes a not-for-profit foundation and two production companies for audio and TV programmes.
By the end of 2020, they had also signed deals with Netflix and Spotify to create exclusive content for these streaming giants.
Earlier this year, it was announced the Duke of Sussex had also been appointed Chief Impact Officer at mental health and coaching firm BetterUp.
Prince Harry briefly spoke about his relationship with Prince William during his interview with Oprah Winfrey
In February, he spoke to his friend and comedian James Corden about why he moved to the US and stepped down as a full-time working royal – while also opening up on Archie and his strong bond with the Queen.
A few weeks later, he and Meghan were interviewed by Oprah Winfrey in a two-hour-long tell-all chat during which they launched damaging claims of neglect and racism against the Royal Family.
Two months later, the Duke chatted again about his life as a royal and his relationship with his close relatives in an episode of the Armchair Expert podcast and in the mental health docu-series he co-created with Ms Winfrey – The Me You Can’t See.
Source: EXPRESS CO UK