Fredericks and Headley Britannia went clear in the show jumping

Headley Britannia jumped a clear round in the show jumping to become the first mare to win at Burghley for 33 years.

Andrew Hoy, who led after the cross-country, had three fences down on Moon Fleet to finish second, with Shane Rose third on All Luck.

"It has all happened for me this week," said Fredericks, who headed an all-Australian first three.

"I was so disappointed not to compete at WEG (The World Equestrian Games) and I never really believed this could happen.

"But she has been a star and I want to say thank you to everyone who has been a believer in this little horse."

If this is the worst day of my life it can't be that bad Second-placed Andrew Hoy

Hoy, who had already won the Rolex Kentucky and Badminton titles, was chasing a Grand Slam of eventing crowns.

"I never had the Grand Slam so I never lost it. I came within 30 seconds of a Grand Slam before I had the second rail down," said Hoy.

"If this is the worst day of my life it can't be that bad."

Cressida Clague-Reading was the highest placed Briton on fourth on Carousel Quest, while Hoy also came fifth on Mr Pracatan.

Carousel Quest was competing at his first four star event and Clague-Reading said she had never doubted the horse's ability to compete at the top level.

"We have always known he had it in him, as I have had him since he was a four-year-old," she said.

"But there no pressure here and we have just made our way up the leaderboard and are thrilled to have done so well with him."