"And I think he's so desperate to please her and go along with whatever she says, no matter how ill-conceived it is. He is that besotted with her."
She added that Markle wears the pants in the relationship - and compared her to Princess Diana.
"She wears the trousers and is as dominating, charming and captivating a personality as Princess Diana was in her marriage," she told the publication.
Lady Colin Campbell says Meghan Markle's intelligence means she dominates her relationship with Prince Harry. Photo / Getty Images
Harry struggled academically, while Markle has a double degree in theatre and international relations from Northwestern University, according to Page Six.
Lady Colin is convinced Markle's move to the US and the couple's exit from royal duties speaks volumes about her future ambitions.
"I know the Duchess of Sussex has political ambitions, and I've been told that one day she wants to run for president."
Colin Campbell became a Lady when she married Lord Colin Campbell in 1974. She retained the title after the couple split after one year of marriage in 1975.
Her biography about Princess Diana, called Diana in Private: The Princess Nobody Knows, was a best-seller when it was released in 1992.