The ad spot is part of Unicef's campaign that launched last month called "Unite for children, unite against Aids" and will be aired today, which is World Aids Day, on CNN and MTV.
The creative features the two stars, who are both Unicef ambassadors, at Beckham's football academy in Los Angeles with a message to raise awareness of the global problem of HIV/Aids for those children who either have the disease or have lost their parents to it.
It also shows the two stars with a piece of blue string, which was developed for Unicef's HIV/Aids promotional work to symbolise that the wearer is tied in to the campaign.
The ad will be made available on Unicef's Aids from December 5, which also gives details of how to join the campaign.
Beckham said: "Every single person can play a role in supporting Unicef's campaign to ensure children get the support they need to prevent HIV/Aids from absolutely devastating their lives, as it has sadly already done for so many millions.
"Robbie and I are proud to be involved in this campaign and hope others will want to unite with us to help children whose lives have been affected by HIV/Aids."
According to Unicef, more than 15m people have lost at least one parent because of Aids. The campaign is calling for urgent action to prevent infection, provide medical support and make treatments more affordable and accessible.
Meanwhile, latest accounts for Beckham's company Footwork Productions show that the football star's powerful brand identity is far from waning, even though he is in the last stages of his football career and has been blighted by speculation about his private life in recent years.
The figures for the firm show that last year the company, of which he is the sole shareholder, made £17,335,937. This includes his wages at Real Madrid and lucrative sponsorship deals, such as contracts with Gillette, Adidas and Pepsi.
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