She continues: "When William called to tell him the good news, Harry let out a string of expletives before telling his brother and soon-to-be-sister-in-law, 'It took you long enough!'"
Despite previous reports of his close relationship with the Royal couple, Clooney went on to dismiss suggestions he could be godfather to their unborn child.
Since Markle and Prince Harry began dating, the duchess has been subject to media scrutiny about everything from her "messy" bun to her troubled relationship with her father.
He explained, "She's a woman who is seven months pregnant and she has been pursued and vilified and chased in the same way that Diana was and it's history repeating itself". "And we've seen how that ends", Clooney added, according to PA.
Clooney, who attended Meghan and Harry's wedding past year alongside his wife, human rights lawyer Amal Clooney, said he had seen the recent coverage about the Duchess's supposed letter. The former actress pulled her hair back in a classy low bun.
They were also the first people to reveal the existence of the letter and said Meghan wrote it in an attempt to mend their rift privately.
Just days before his daughter was due to marry into the royal family, Mr Markle was caught staging paparazzi photos of himself.
They mentioned a five-page letter she wrote to her father, Thomas Markle Sr.
Meghan has also faced intense interest from the unsparing United Kingdom press since her engagement to Prince Harry was announced in 2017.
"While the objective of Meghan's letter was very much to fix the relationship with her father, she knew in her heart of hearts that this was going to be released to the papers", he said.
Over the weekend, a deeply personal letter allegedly written by the duchess to her father in August, was published - months after he missed her wedding.
The former Hollywood lighting director, who lives in Mexico, said that he never meant to make the handwritten letter public "out of respect for Meghan" - but says he has been forced to do so now because its contents have been falsely portrayed.