Clooney, 57, said history was repeating itself in the case of Meghan and Diana, warning "we've seen how that ends".
But Samantha said she would "challenge her to take a lie detector test anywhere on the planet", after Meghan criticised Thomas for ignoring her and Prince Harry's offers of help after he was unable to attend their wedding in May following heart surgery.
One unnamed friend told the publication that members of her inner circle "worry about what this is doing to her and the baby. One should never assume", the royal wrote.
Meghan pictured with her father Thomas Markle in happier times.
George Clooney has spoken out to defend the Duchess of Sussex.
"They're just chasing Meghan Markle everywhere, she's been pursued and vilified", Clooney told reporters at an worldwide press panel for his forthcoming Stan series Catch-22 in Pasadena, California on February 11.
Crash victim says Prince Philip is right to give up driving
According to reports, the Duke of Edinburgh was subsequently offered " suitable words of advice " by a Norfolk police officer. Philip retired from public life in 2017, although he still occasionally appears with his 92-year-old wife at official events.
"You're taking a letter from a daughter to a father and broadcasting it everywhere".
She said that there is nobody else in the world that can make her laugh as much as Prince Charles' ex-wife did.
"Some narcissists were "only children", others... wish they were", she said on Twitter, replying to a post about Meghan.
Kensington Palace offered a pointed statement first confirming Harry's relationship with Meghan in 2016.
Meghan was wearing Ralph Lauren in the photo and as Violet was working for the designer, she told Harry that the Hollywood star was in the country.
Meghan's messages to the vulnerable women during her visit on February 1 read, in capital letters and often followed by a heart: "You are strong", "You are special", "You are brave" and "You are loved".