The Hollywood star is a close friend of Harry and Meghan and he and his human rights lawyer wife Amal attended the royal wedding in May a year ago as well as reportedly visiting the couple at their Cotswolds home.
The duchess also criticized her father for the lies of his "other daughter" ― Samantha Grant, who is the duchesses' half-sister. "She's been pursued and vilified", he said. Every time it gets cold like this, I take them to the guard stations. I love you, I have one father.
Clooney's comments come shortly after a newspaper published a letter allegedly written by the duchess to her father in August, months after he missed her wedding.
According to The Telegraph, Palace aides are considering whether to take a stand over the very public family disclosures, taking legal advice before the Duchess decides whether she wishes to take formal action.
In her signature cursive handwriting, the letter begins, "Daddy, it is with a heavy heart that I write this, not understanding why you have chosen to take this path, turning a blind eye to the pain you're causing".
Thomas, 74, branded Meghan's lengthy letter a "dagger to the heart" and dismissed her claims, showing the newspaper texts he believes prove he'd made attempts to communicate with his pregnant daughter and her spouse.
In the deeply personal missive, Meghan accuses her father of breaking her heart "into a million pieces" by giving interviews to the press, fabricating stories and attacking her new husband. "I begged you to accept help - we sent someone to your home...and instead of speaking to me to accept this or any help, you stopped answering your phone and chose to only speak to tabloids".
A number of the Duchess' close friends recently spoke out in support of her following a surge of negative press and comments.
One unnamed friend told the publication that members of her inner circle "worry about what this is doing to her and the baby".
"I am a passionate supporter of BAFTA and I couldn't be more proud of its ambitious plans to dramatically increase the support for new talent over the coming years". "You can hate me if you want", he wrote.