Moments earlier she had been laughing and joking with her aunt the Duchess of Cornwall.
But in a matter of seconds, Zara Phillips' hand flew to her mouth, her face transforming into a picture of concern.
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The keen equestrian had just seen her ex-boyfriend Richard Johnson fall from his horse at the Cheltenham Festival.
Camilla, standing next to Zara in the royal box, also looked on in shock as the jockey's horse fell on it's rider, crushing his left leg.
The 34-year-old was lifted into an ambulance, in visible pain, and taken for emergency treatment.
A racing official said the rider was "obviously shaken" but was recovering well after only suffering a strain.
"He had a lucky escape because it looked like a terrible fall," added the official.
Zara and Richard dated for five years before splitting in 2003.