Meghan Markle is suing a British newspaper for publishing her personal letter, according to BTA news agencies.
In an emotional statement, Prince Harry said he and his wife had taken legal action in response to what he described as "ruthless" treatment by some sectors of the British press.
"Though this action may not be the safe one, it is the right one."
Megan Markle gave birth to a boy. The news was reported by Prince Harry, who was joyfully tired of television cameras, Sky News reported.
"It was incredible, thank you for your support, we're still thinking about the name," said Prince Harry.
Earlier from the Buckingham palace, Megan Markle had arrived in her maternity ward this morning with her husband.
Over six million people tweeted on Prince Harry's marriage to Meghan Markle, more than three times the number during his older brother's wedding, social media monitoring firm Visibrain said May 20.
Meghan Markle is not the first American actress to give up her career for the love of a prince. More than six decades ago her fellow countrywoman Grace Kelly walked away from Hollywood to take on a new role as princess of Monaco.
A waxwork of Meghan Markle wearing a replica of her diamond engagement ring was unveiled on May 9 at London's Madame Tussauds museum, less than two weeks before her wedding to Prince Harry.
After nearly 70 years of producing royal merchandise, British luxury gift manufacturer Halcyon Days is hoping the upcoming wedding of Prince Harry and his U.S. fiancée Meghan Markle will be a happy one for them as well as the bride and groom.
Prince Harry and Meghan Markle's wedding will be held on Saturday 19 May 2018, Kensington Palace has announced, quoted by BBC.
The couple confirmed their engagement last month and said the ceremony would take place at St George's Chapel, Windsor Castle.
The Royal Family will pay for the wedding, including the service, music, flowers and reception.