Britney Spears dress on eBay

Britney Spears is helping a friend's sick son by selling off a famous dress on eBay.

It's the silver backless dress which she wore in the ads for her fragrance Radiance. All the money raised is going to the The Matthew Van Daff Special Needs Trust.

Matthew, was born with a brain injury after being starved of oxygen in the final days of pregnancy. The proceeds raised from the sale will help his parents provide round-the-clock care for their son.

On Britney's page, her assistant posted, "Such a great cause. Brit donated her dress from the Radiance ad to our friend David, who started a trust for his son with a brain injury. He put the dress up for auction & all proceeds will go to his son's cause."

Britney will be hoping to top the Vodafone Freebees Big Top 40 chart this weekend with her new single Hold It Against Me.