Zara Phillip retired from competing at the Badminton Horse Trials after making a mistake on the cross-country course.
After a good start during yesterday's dressage stage, Phillips - who was riding High Kingdom - missed the second of two brush jumps in the Lake and pulled up.
It means she can no longer take part in tomorrow's show jumping stage.
More top news
A man who hit a 13-year-old boy leaving him bedbound for life has been jailed for three years.
Migrants as young as 10 have been attacked by French police and armed civilian "militias" in Calais in recent weeks, a charity has claimed.