For decades, Princess Mary has leaned on her best mate Amber Petty – from asking her to be a bridesmaid at her 2004 wedding through to inviting her on family holidays with her husband Prince Frederik and their four children.
But Woman's Day has learned that Mary, 48, is finding herself feeling that it's "increasingly harder to maintain a friendship" with her Melbourne-based friend, and it's not just because she's thousands of kilometres away in Copenhagen.
"Amber has been talking nonstop about Princess Mary and taking it a little too far for her comfort," says a source.
"She has her memoir coming out soon, and Mary is worried she's going to feature in it way too much."
Indeed, recently on Australian TV Amber shot an arrow through the widely believed story that Mary met her prince during a chance encounter over margaritas at Sydney's Slip Inn pub during the 2000 Olympics.
"I'm sorry to break everybody's hearts, but it is not always about randomly running into princes in pubs," she said during an appearance on Sunrise.
"It wasn't just a random meeting... it was an organised small dinner during the Olympics and Mary happened to be invited, and most of the other guests happened to be royals. That's really the truth. It's not what you know, it's who you know."
Amber, 49, added that Mary and Fred sat across from each other and developed a "really lovely connection".
While Mary herself has never publicly confirmed the story, sources say she was "very upset" with Amber for going on the record about something so private.
"Whether or not the Slip Inn story was true, that's how a lot of Mary's fans think it went down, and Mary certainly doesn't want to be seen as having deceived them," says a source.
"There was no need or reason to bring up something like that at all."
The Hobart-born royal was also "distressed" to hear Amber has been confessing to the press that being a bridesmaid to your best friend-turned-princess wasn't the joyful occasion everyone believed it to be.
The Danish press reports Amber claims "her friendship changed" with Mary after the wedding, and her move to Denmark "affected their relationship and their life".
Indeed, in August, she confessed, "Losing my best friend in a sense, I mean we are still really close... but losing her after the wedding was a difficult 10 years."
Amber has since turned to the spiritual world because she "wasn't in a good emotional space", blaming it partly on her lack of luck in finding love.
She has opened The Tarot Tea House in Melbourne, where she works with a group of tarot readers.
"Those surrounding Mary think it's very unfair that Amber is telling the media about personal things involving the princess," says a Danish royal source.
"Mary is extremely private, and this must be upsetting her a lot. Plus, even though it could just be a coincidence, she can't help but find the timing of the whole thing a little hard to swallow, given Amber has a book coming out and a tea house to promote.
"Of course Mary is sad that her friend is having such a rough time, partially due to the extra attention she gained from being her bridesmaid, but there must be a better way to deal with it than this."