Kate Middleton is no longer ‘the sister Prince Harry never had’ as days of friendship are ‘long past’, expert says

KATE Middleton is no longer "the sister Prince Harry never had", a royal expert has said.

The Duchess of Cambridge formed a close friendship with the Duke of Sussex while he was a working royal, teaming up on a number of projects.

Harry famously described Kate as "the sister he never had" and together with Prince William and Meghan Markle, the two couples were known as the Fab Four.

But the group's relationship appeared to breakdown when Harry and Meghan quit royal life - and Kate and Harry's friendship is now said to be "long in the past".

Speaking to OK! Magazine, Royal commentator Duncan Larcombe said: "Kate was, as Harry said, the sister he never had and clearly that is not the case any more.

"There was a time when Harry would have been instrumental in any celebrations or any fun that the couple were having, but those days are long in the past."

It comes ahead of Kate's 40th birthday on January 9, expected to be a "low key" event.

And with Harry thousands of miles away in California, it's unlikely he will be heavily involved.

Of any potential celebrations, Duncan added: "It will be very interesting to see what messages Harry and Meghan send Kate.

"This is the problem, as the rift continues, as the war between the boys seems to show no sign of finishing, days like Kate's 40th birthday milestone immediately become events that can be contrasted with how it used to be."

Kate was previously said to bring out Harry's "fun side", with the pair showing a "strong bond" when Harry lived in the UK.

In his best man's speech for his brother's wedding, Harry reportedly joked he gave Kate the thumbs up for having "killer legs".

But William has since called his wife the "peacemaker" between the brothers, with Kate stepping back at Prince Philip's funeral to allow them to speak.

It is not yet known how Kate will celebrate her birthday, which comes just a few months after Meghan celebrated her 40th in August.

The Duchess of Sussex released a glitzy comedy video with Hollywood actress Melissa McCarthy for hers - and in it launched a new initiative called 40x40.

Duncan, however, said he does not expect Kate to follow suit and it's unlikely the Duchess of Cambridge will announce anything.

He said: "Kate and William are not the sort to go away to celebrate on their own and leave the kids at home.

“I think the same will apply to Kate’s birthday as it does to Christmas - it will be low key and it will be focused entirely on the family.”