Michelle Obama was among those to send their congratulations after the Duke and Duchess Of Sussex welcomed a baby boy.
A visibly delighted Harry spoke at Windsor Castle’s Royal Mews and said Meghan gave birth to a “very healthy” son on Monday morning.
Following the news, celebrities and famous figures from Los Angeles-born Meghan’s native country sent their best wishes.
Ms Obama, the wife of former US president Barack Obama, was among those to send her congratulations.
She tweeted: “Congratulations, Meghan and Harry! Barack and I are so thrilled for both of you and can’t wait to meet him. #RoyalBaby.”
President Obama retweeted the message.
Patrick J Adams is best known for starring alongside Meghan in the US legal drama Suits. The actor suggested his seven-month-old daughter could be a friend of the royal baby.
He wrote on Twitter: “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.”
The Suits official Twitter account replied to Royal Family’s tweet announcing the birth and wrote: “The entire #Suits family sends their congratulations to The Duke and Duchess of Sussex, Prince Harry and Meghan Markle, on the birth of their baby boy!”
US chat show host Ellen DeGeneres also sent her congratulations via Twitter.
She said: “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”
It was not just stars from the US who sent their congratulations.
Former One Direction star Liam Payne said: “Congratulations to the Duke and Duchess of Sussex on the birth of your baby boy. So happy for the both of you.”
However, Good Morning Britain host Piers Morgan was not among those celebrating the birth, instead saying he was struggling to “muster up a semblance of enthusiasm” for the occasion.
He said: “Trying, but currently failing, to muster up a semblance of enthusiasm for this royal baby story before tomorrow’s @GMB. Hopefully Meghan will announce her son is identifying as a gender-fluid vegan before we go on air.”