Princess Anne and Sir Timothy Laurence tied the knot almost 30 years ago in Balmoral back in 1992 and have been married ever since.
While it is not the Princess Royal's first marriage after she was previously married to Mark Philips whom she shares her two children Zara and Peter with, Anne and Sir Timothy are notoriously unaffectionate in public - even less so than King Charles and Queen Camilla.
It's likely their older age might have something to do with their lack of outward warmth towards each other, especially compared to other younger royal couples such as Princess Kate and Prince William and Mike and Zara Tindall.
However, according to one body language expert Judi James, the senior royal has always seemed "stoic" and "restrained"- even on her own wedding day.
The Express reports that Judi analysed Princess Anne and Timothy's relationship and came to the conclusion that the Princess Royal has a "near-allergy to public displays of affection".
Judi told the publication: "It is almost hilarious how dissimilar Anne and daughter Zara are when it comes to PDAs.
"Zara is one of the most spontaneously tactile members of the royal family, hugging anyone she cares for and especially tactile and affectionate with her uncle Charles, who resembles his sister in terms of his near-allergy to PDAs.
"Anne is right down one end of the PDA scale. Stoic, emotionally reserved and clearly considering being royal as synonymous with restraint and composure, she is so non-tactile with her husband Tim in public that it’s hard to remember when, if ever, they were seen to exchange as much as a glance or a couple of words."
The expert suggested that Anne's unaffectionate behaviour is not just displayed in their lack of visible touch and endearment but also in their stance around one another.
Judi claims that a lot can be said about the Princess Royal's relationship just by the way she stands around her husband of 29 years.
She explained: "Tim often stands or walks behind his wife and when they are together there are no tie signs or touch.
"Even on their wedding day the royal fans were left starved of any signs of romantic affection between the bride and groom and it was joked at the time that it was hard picking them out as a couple."
However, while the Princess may have always come across as a more private individual in terms of her romantic relationship, the body language specialist argued that this hasn't always been the case in all aspects of her life.
Ms James claims the royal showed "glimpses" of a more "earthy version" of herself in her younger years, especially when her late aunt Princess Margaret was around as a role model to her.
Judi said: "For Anne growing up in a generation of royals who considered the hands-off approach to be appropriate, the idea of being relaxed and tactile in public would have been unthinkable.
"But she did grow up with Princess Margaret as one of her role models and there were often glimpses of a much more earthy version of Anne lurking below the rather frosty surface."
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