The Princess Royal, the president of the Riding for the Disabled Association (RDA), will be the guest of honour at the association’s 40th anniversary celebrations next month.
More than 25,000 adults and children benefit from the RDA’s provisions for riding and carriage driving.
The Princess will cut a commemorative ribbon and cake at Chigwell Riding Trust in London to launch RDA’s The World’s Biggest Riding Lesson on 30 September.
The event aims to unite riders across the world as they participate in a set riding lesson on the same day.
She will also draw the anniversary raffle and present awards and rosettes to RDA volunteers and riders.
RDA chief executive, Ed Bracher said: “Her Royal Highness has inspired and encouraged thousands of RDA volunteers and riders who have met her.
“This is a great year for the RDA and we are delighted that the Princess is joining in the celebrations.”