Britain's Prince Harry and Meghan, Duchess of Sussex. (Dominic Lipinski/Pool via AP, File)
Patrick J. Adams, Michelle Obama, and Ellen DeGeneres are among those to have congratulated Prince Harry and Duchess Meghan on the birth of their son.

Adams congratulated his former 'Suits' co-star, Duchess Meghan, and her husband Prince Harry, after their son was born on Monday and admitted he can't wait for the tot to meet his and wife Troian Bellisario's little girl.

He tweeted: "Just heard that the world just got heavier by 7 pounds and 3 ounces. Much love to him and his incredible parents. Learned first hand 7 months ago how transformational becoming a parent is and couldn't be happier for Meghan and Harry as they begin this adventure. #playdatesoon.(sic)"

Harry's uncle, Prince Andrew, was one of the first members of the royal family to share a message of congratulations.

He wrote on Twitter on Monday afternoon: "Congratulations to The Duke and Duchess of Sussex on the safe delivery of your baby boy!"

Another of the 34-year-old prince's uncles, Charles Spencer - the brother of Harry's late mother Princess Diana - sent his congratulations via Twitter.

He wrote: "Really very lovely news today - many, many, congratulations! (Good to have another Taurean in the family....) (sic)"

Meghan's good friend and make-up artist, Daniel Martin, told his followers he is a "proud guncle" as he retweeted an official announcement about the birth of the boy, whose name has not yet been revealed.

Former US First Lady Michelle Obama and her husband, ex-President Barack Obama, "can't wait" to meet the baby.

She tweeted: "Congratulations, Meghan and Harry! Barack and I are so thrilled for both of you and can't wait to meet him. #RoyalBaby. (sic)"

Talk show host Ellen DeGeneres also used Twitter to congratulate the royal couple.

She wrote: "The #royalbaby is here! Congratulations, Meghan Markle and Prince Harry. The baby is 7th in line for the throne, which is crazy, because right now I'm 7th in line for the key-making kiosk at my grocery store. @RoyalFamily.(sic)"

UK Prime Minister Theresa May sent her best wishes to the family.

She tweeted: "Congratulations to the Duke and Duchess of Sussex on the arrival of their baby boy. Wishing you all the best at this happy time." 

Harry and Meghan, 37, used Instagram to announce the birth of their son.

A post titled "It's a boy", was captioned: "We are pleased to announce that Their Royal Highnesses The Duke and Duchess of Sussex welcomed their firstborn child in the early morning on May 6th, 2019. Their Royal Highnesses' son weighs 7lbs. 3oz.

"The Duchess and baby are both healthy and well, and the couple thank members of the public for their shared excitement and support during this very special time in their lives.

"More details will be shared in the forthcoming days."