Michelle Obama at London's Royal Festival Hall. Ten people have been disappointed.
There were 40,000 people in the tickets queue.
The former US First Lady is appearing at the 2,900-seat venue on 3 December.
Tickets are appearing on Viagogo for thousands of pounds, but the venue has been removed.
Any third party will not admissable, the venue said.
Obama wants to be discussing her memoir, Becoming, with award-winning novelist Chimamanda Ngozi Adichie.
They will talk about her experiences from childhood, her work, motherhood and "her time spent at the world's most famous address".
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She wants to share "life lessons learned" while hoping to "inspire people to become the very best version of themselves".
People tweeted that they had been queuing since 4am at the venue.
The South Bank Center, which is a multi-arts venue next to the River Thames, was tweeted at 10:30 GMT to say they had sold out.
The London date is in the middle of a 13 night tour starting on November 13 in the Obama's hometown of Chicago, where she will be in conversation with Oprah Winfrey.
Tickets sold almost in the US and Obama she tweeted "What a great way to travel to my upcoming book tour".
The South Bank Center said they are in the process of identifying touted tickets.
They told the BBC that due to "extreme demand for this event, unfortunately there will be people who are disappointed".
But they added they had worked out to be as easy as possible, by limiting themselves to a lower price point of £ 30. "
In London and the UK, as well as local charities, three hundred tickets have been brought to school.
The South Bank Center said they have not been able to do much to get tickets.
10am today. 10am today.
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