Prince Harry's memoir 'Spare' has become the fastest-selling non-fiction book ever, Guinness World Records confirmed. It broke the record previously held by US ex-President Barack Obama's 'A Promised Land'. Around 1.4 million copies of 'Spare' were sold during first-day sales in the UK, US, and Canada, while around 887,000 'A Promised Land' copies were sold on release day.