The two women will split the prize after judges defied 1993 rule change that only one author could be honoured.

Margaret Atwood’s The Testaments and Bernardine Evaristo’s Girl, Woman, Other jointly won the Booker Prize on Monday in a surprise double award of Britain’s most prestigious literary prize.

The authors will split the 50,000 pounds ($62,800) annual prize, the judging panel said.

The award honours “the best novel of the year written in English and published in the UK and Ireland”.

The Testaments, published last month, is the sequel to 79-year-old Atwood’s best-selling 1985 novel, The Handmaid’s Tale. The Canadian author previously won the prize in 2000 for The Blind Assassin.

In Girl, Woman, Other Evaristo, the first black woman to win the Booker, tells the stories of 12 characters living in Britain, mainly female and black aged 19 to 93.

While the prize has been jointly awarded twice previously, the rules changed in 1993 limiting the award to one author. The judges defied those rules, saying they could not agree on a winner between the two books, which were on a shortlist of six.

“Neither of us expected to win this,” Atwood, who becomes the oldest person ever to win the Booker, said in her acceptance speech in a televised ceremony.

“I would have thought that I would have been too elderly and I kind of don’t need the attention so I’m very glad that you’re getting some … It would have been embarrassing if I had been alone here,” she said to Evaristo.

Atwood’s book, eagerly awaited by fans, returns to the totalitarian state of Gilead some 15 years after the end of The Handmaid’s Tale, telling the story of three women.

Atwood has said a deterioration in women’s rights in some parts of the world including in the United States prompted her to write the sequel, described as a “savage and beautiful novel” by the judging panel.

In Britain, it was an immediate hit, selling just over 100,000 hardback copies in its first week of release.

The bleak dystopian The Handmaid’s Tale, where women are banned from reading and writing and those that are fertile are forced into sexual servitude, was itself nominated for the Booker Prize.

Girl, Woman, Other is Evaristo’s eighth book of fiction, and was described by the judges as “a must-read about modern Britain and womanhood”.

“This is incredible. I suppose a lot of people say, ‘I never thought it would happen to me,’ and I will say I am the first black woman to win this prize,” the British author, 60, said to loud applause.

“I hope that honour doesn’t last too long. I hope that other people come forwards now,” she said.