Prince William and Prince Harry missed the Epsom Derby on Saturday due to their military commitments.
The future King, an RAF search and rescue pilot, was undertaking exams for his flying captaincy.
Meanwhile, his brother, who is an Apache helicopter pilot, was in training for his deployment later this year – probably to Afghanistan.
Both William and Harry are committed to balancing their military positions with serving their grandmother and royal duties.
During his tour of Brazil in aide of the Diamond Jubilee, Prince Harry said: "We’ve both got our military careers, and that’s what we’ll continue to do.
"I will help out with my grandmother whenever she needs me, but I have this job that does suck up a lot of my time, and that’s the number one for me."