Princess Anne, 71, has been patron of the Scottish Rugby Union since 1986, while Prince William, 39, is patron of the Welsh Rugby Union.
The Queen's only daughter was present at the match at the Principality Stadium in Cardiff on Saturday, alongside her husband, Vice Admiral Sir Tim Laurence.
WATCH: Mike Tindall gives his very honest verdict on Kate Middleton's rugby skills
Dressed in a tartan trouser suit, the royal also met members of the Welsh Rugby Charitable Trust before the match.
Unfortunately, there was disappointment for Anne as Wales beat Scotland 20 – 17, and while William didn't attend the match, we wonder if there was a bit of healthy competition between him and his aunt over the weekend?
Anne's son-in-law and former rugby star, Mike Tindall, recently revealed that the younger royals keep in touch with each other in a family WhatsApp group. William's wife, the Duchess of Cambridge, has just been announced as patron of the Rugby Football Union and the Rugby Football League, and Mike revealed he had wanted to tease his cousin-in-law about her sports skills.
The Princess Royal attended the rugby match in Cardiff
Earlier this month, Kate joined an England rugby training session at Twickenham Stadium and Mike was quick to share his verdict on his podcast, The Good, The Bad & The Rugby, last week.
"I text Ellis [Genge] and said, 'Mate, please tell me anything she messed up on' so I could sort of… family WhatsApp group, get to her, and he said, 'No she was actually pretty good, and she was really good at kicking,' and I was like [sighs]. But she has this competitive nature," he said.
Mike added of Kate: "Just imagine, anyone who's ever tried it, getting thrown up in the line-out if you've never done it before is not easy because normally, you'll kick the prop in either the nuts or the face as he's lifting you and she just looked effortless.
"The best thing is when it rolls to England and Wales, we get the battle of the Cambridges."
Princess Anne met members of the Welsh Rugby Charitable Trust
There's a chance we could see William and Kate get competitive later this month as Wales will take on England at Twickenham on Saturday 26 February in the Guinness Six Nations 2022.
Meanwhile, Mike joined his mother-in-law Anne at England's first Six Nations match against Scotland at BT Murrayfield in Edinburgh on 5 February.
Scotland were victorious, winning 20-17 against Eddie Jones's side.
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