The trio told the duchess about their journey in a 30-minute talk, revealing they suffered from cramps during the trip and struggled to walk straight once they'd completed their challenge.
They also presented Camilla with a flask and a fleece and Kat - who has cervical cancer - joked the duchess "may take up rowing" following their chat.
Camilla also came face-to-face with her "fictional alter ego" on Wednesday.
Emerald Fennell - who played the younger duchess in two seasons of The Crown - laughed and joked with the royal at the reception.
But Camilla claimed she found it "very reassuring" to know that Fennell was among the guests at the reception.
She quipped: "For me, it's very reassuring to know that if I should fall off my perch at any moment, my fictional alter ego is here to take over. So, Emerald - be prepared!"
- BANG! Showbiz