Kate, Princess of Wales and Crown Princess Mary have a "natural rapport" that echoes Queen Elizabeth II and Margrethe II, a royal commentator has claimed.
Australian-born Mary, 51, will become the Queen of Denmark on Sunday, while her husband Frederik will become the King.
This comes after Queen Margrethe II announced her surprise abdication on New Year's Eve.
Since marrying into the British Royal Family in 2011, it has been widely reported that Kate modelled her fashion and body language heavily on Crown Princess Mary.
Kate and Princess Mary have a 'natural rapport' that echoes Queen Elizabeth II and Margrethe II
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Queen Margrethe and Queen Elizabeth II together in 2000
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Gareth Russell, a royal author who published The Palace: From the Tudors to the Windsors, 500 Years of Royal History at Hampton Court, exclusively spoke to GB News about Mary's British roots and whether or not this will impact the relationship between the two monarchies in the future.
Mary Donaldson was raised in Australia but her parents were originally from Scotland.
Russell said: "Crown Princess Mary already has quite a close friendship with the Princess of Wales.
"They share a lot of the same interests and it's been commented upon by a lot of observers and journalists when you see them together during state or official visits, that there's quite a natural rapport between the two of them.
Crown Princess Mary photographed with Princess Kate in Denmark in 2022PA
Queen Margrethe and Queen Elizabeth II pictured giggling in 2014
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"Crown Princess Mary is often referred to as the 'Kate Middleton of Denmark'. She's an immensely popular figure with the Danish public.
"Broadly speaking, the Danish Royal Family have very high approval ratings and even within that, Crown Princess Mary has exceptionally high approval ratings."
Russell believes that Mary and Kate will echo the relationship between Queen Margrethe II and Queen Elizabeth II.
He continued: "We can expect a close relationship between the new King Frederick X and Queen Mary and the Prince and Princess of Wales, which will continue the very close ties between the two monarchies that we saw with Queen Margrethe II and Queen Elizabeth II.
Crown Princess Mary and Princess Kate photographed together in 2011
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Princess Mary and Prince Frederik will be Denmark's next King and QueenReuters"Those two used to use familiar nicknames for each other.
"Queen Elizabeth II called the Queen of Denmark Daisy, and she called her Lilibet.
"So it will be continuing on those close ties."
On Sunday, Frederik and Mary will become the King and Queen of Denmark, while Margrethe will step down from the throne after 52 years.