In was the 30th edition of the European Eventing Championships, first time held 1953 at Badminton House.
She died in 1987, aged 90 at Badminton House, Gloucestershire.
Badminton House also gives its name to the sport badminton.
A spokesman for the duke's estate at Badminton House responded: "We do not want to comment about a private transaction."
Badminton House is also very strongly associated with fox hunting.
Beaufort died in 1984, aged 83 at his seat, Badminton House.
Beaufort died and was buried in 1853, aged 61 at Badminton House, Gloucestershire.
Lady Helena survived her husband by 37 years and died at Badminton House, home of her sister.
Beaufort died and was buried in 1924, aged 77 at Badminton House, Gloucestershire.
The sport got its name because it was a popular activity at the Duke of Beaufort's country seat: Badminton House.
