The event was held up for about 20 minutes.
Spring Along, 18, is suspected to have also broken his neck when he fell on top of the first step. He was dead when veterinarians arrived at the fence. Berkeley sustained cuts and bruises in the accident.
Spring Along had represented Britain four times at senior level. The bay Irish gelding won the British Open title at Gatcombe's Autumn event with Berkeley. The combination completed Badminton six times and was third in the four-star event last year. He was due to be retired at Badminton this year. He was also fourth at Barbury Castle (CIC3*) last year.
Spring Along - known as "Pod" at home - was owned by Daisy Berkeley and her mother, Caroline Dick.
British Eventing's Chief Executive, Mike Etherington-Smith said: "It really is such sad news. Spring Along was one of the best Event horses of recent times, his fantastic record speaks for itself. Our thoughts are with Daisy, her mother Caroline and all involved with this fabulous horse."
Daisy Berkeley and Spring Along on the course at Gatcombe just before their accident.
© Lulu Kyriacou
Spring Along's major placings and achievements:
1st British Open Championship, Festival of British Eventing
4th Barbury Castle CIC3*
3rd Badminton CCI4*
4th Blenheim Palace CCI4*
1st Gatcombe Park Advanced
1st Barbury Castle CIC3*
6th Badminton CCI4*
2nd Barroca CIC3*
Team Bronze Beijing Olympics
14th Barbury Castle CIC3*
Completed Badminton CCI4*
Team Gold & 7th Individual European Championships, Pratoni del Vivaro (Italy)
8th Festival of British Eventing CIC3*
8th Barbury Castle
Completed Luhmuhlen, Germany CCI4*
Team Silver & 12th World Equestrian Games Aachen, Germany
2nd Barbury Castle CIC3*
8th Badminton CCI4*
Individual 11th Place European Championships, Blenheim Palace
8th Badminton CCI4*
14th Burghley CCI4*
11th Badminton CCI4*
13th Blenheim Palace CCI3*
Completed Boekelo, Netherlands, CCI3*
Completed Thirlestane, Scotland, CIC3*