The shorts cost 50p in an Oxfam shop two years ago.
But they're now expected to raise hundreds of pounds when they go on sale at the auction on 18 April.
A walk-on part in the next S Club video could also be yours for the right price!
Ronan Keating will be performing live at the event at London's Alexandra Palace.
All money raised will go to the Woolworths Kids First charity which helps children in local communities.
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