Captured by PEOPLE magazine's Simon Perry, the Duchess of Sussex seemed to innocently forget the "duchess slant", which is when royal women cross their legs at the ankles or put both legs off to the side to maintain poise and posture.
Taking her seat beside Prince Harry and Queen Elizabeth, Meghan accidentally crosses her legs, but quickly and effortlessly recovers uncrossing her legs a the knee and slanting them to the side.
Proper etiquette dictates that royal women keep their legs and knees together, although crossing at the ankle is also acceptable.
Meghan expertly demonstrated the "duchess slant" at the first solo outing with the Queen earlier this month.
The newlywed couple joined Queen Elizabeth II at Buckingham Palace to celebrate a group of young leaders from across the world.
The 92-year-old monarch hosted an evening reception for change-makers across the Commonwealth of 53 nations.
Harry was named as the organisations Youth Ambassador late last year.
The 33-year-old Duke of Sussex addressed the Queen's Young Leaders, a group of emerging influencers ages 18-29, and said: 'I guess you can say you’re stuck with me.
"I, together with my wife Meghan, look forward to convening young people from around the Commonwealth to hear your ideas, work with you to build platforms for you to collaborate and form partnerships, and continue to meet with many of you as we travel around in our work on behalf of the royal family.
"We look forward to meeting many of you this evening — but we also hope to see you in action in your home countries someday too."