updated 06/07/2014 AT 3:00 PM ET
•originally published 06/07/2014 AT 4:30 PM ET
The royal was supporting his big brother, Prince William, as they held up placards to start the countdown to a new campaign to save wildlife.
William and ex-soccer star David Beckham are set to unite in London on Monday to kick off a crusade that uses the power of sport to raise awareness of conservation issues.
On Friday, the princes signaled the launch of the #WhoseSideAreYouOn campaign by holding up the signs that simply show the date and are signed by each prince.
The organization is a collaboration among seven of the world s foremost conservation organizations and the Royal Foundation of the Duke and Duchess of Cambridge and Prince Harry. Aiming to engage and inspire young people at what the charities believe is a critical time, this latest campaign enlists the help of high-profile sports stars like Beckham and tennis star Andy Murray.