Michelle Obama was joined by David Beckham at a sporting event to urge youngsters to stay healthy and "believe in" themselves.
The pair joined forces at a Let's Move event at the US Ambassador's residence at Winfield House, Regents Park, where around 1,000 American and British children played a variety of sports before gathering to hear the First Lady speak.
A casually dressed Mrs **Obama jogged past rows of excited schoolchildren on to the stage, accompanied by the University of Florida Gator Marching Band who were playing their "fight song".
After telling the crowd she was "so excited" to be there, she turned to the US athletes standing behind her, who between them have won dozens of Olympic medals, and said: "You're not born an Olympian, right?"
She told the youngsters: "In fact, many of them started out just like you, just playing. What they did do is they stuck with it. When they got tired and frustrated or fell short, they didn't give up."
Earlier Mrs Obama gave her own personal good luck message to Team USA. She urged America's athletes to "have fun, breathe a bit, but also win", as she met them at their training base in east London.
The First Lady is leading the US presidential delegation which includes a ringside seat at tonight's ceremony.
She said: "Wow, I'm going to be saying that a lot over the next few days. Wow, wow! I can't believe I am here, I am beyond proud.
"Thank you so much, it's a pleasure and a joy and an honour for me to be here with all of you. I can't begin to tell you how amazing it is for me to be leading the delegation."