In an interview with Royal Box, Frank explained, "Meghan is a complete firecracker of a girl - a throwback to the days of The Queen Mother and Princess Margaret. We've got a big showstopper there.
"A huge contrast with Kate, who's very elegant and very dignified.
"Diana really warmed to people who were relaxed with her. Hopefully she could have got Kate to relax a bit more."
And it sounds like Debbie has a favourite of the two women.
"They don't have much in common except they married two brothers and have married in this role - this job," she explained, adding, that Megs is "very similar" to Lady Di.
"Meghan's a tour de force; she's all about the Meghan Markle brand. She's a very different person from Kate.
"Kate's a person who's careful and cautious; she's going to do things properly and slowly and think about them."