Tickets for Gary Barlow's two solo shows sold out in minutes after they went on sale Friday (October 28).
The singer, who is currently a judge on this year's X Factor, will play London's Royal Albert Hall on December 5 and 6.
All money raised from the two shows will be donated to the Princes' Trust charity.
Speaking about the reaction to the concerts, he said: "I've been overwhelmed at the response for both shows which sold out on Friday.
"Fans will be glad to know we've kept some back with great views of the stage to auction off to the highest bidder so we can make as much money as we possibly can for The Prince's Trust."
The public will now be able to bid for the last few tickets on Barlow's official Gigs and Tours page, with the auction due to close at 8pm on November 2.
There are 200 tickets available for the December 5 show and 300 for December 6. Bidders will be limited to one or two tickets.
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