The stunning royal wore a gorgeous crisp white blazer from Zara with her hair in her signature long waves and could be seen cheering on the English team from the stands, along with many other fans.
Keep reading to see some of Kate's best moments at the nail-biting event...
Kate's arrival
The Princess wore a stunning white blazer and dark trousers for her arrival at the match between England and Fiji, which was held at the Stade Velodrome in Marseille.
While royal watchers had wondered if she might attend with some of her children, Kate arrived alone.
The Princess greets fellow guests
Kate appeared to enjoy a conversation with her seatmate, Sir Bill Beaumont CBE, the Chairperson of World Rugby.
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Kate singing the national anthem
The Princess always heartily joins in with the pre-match tradition, and Sunday was no exception.
The Princess enjoying the game
Kate clapped for both teams as she watched the hard-fought quarter-final match on Sunday.
Kate takes centre stage
Kate, who is a huge fan of rugby, has been attending more events without her husband and seeming ever more confident in her royal role since becoming Princess of Wales.
Half-time pride
Half-time saw England in the lead and the Princess was all smiles at the 21-10 scoreline in her home team's favour.
Kate's keen observations
The mum-of-three appeared to be sharing her insights into the game with her seatmates as England played Fiji, and the latter team started to fight back.
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Extroverted Kate
The Princess enjoys meeting and chatting with people and showed her sociable side on Sunday as she appeared to be relishing the event.
England battles on
The Princess was no doubt on the edge of her seat as Fiji started to catch up with England and they fought to keep their lead.
Princess Kate's generous support
While supporting her local team, the generous-hearted royal always recognises both sides' efforts in high-quality international matches, and being so athletic herself, understands the hard work it takes to succeed.
A winning result!
England held onto their lead, winning the match 30-24, and the Princess beamed at her home team's triumph. We're sure they appreciated her support!
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