The woman, who identified herself as a Belarussian named Natascha, told The Daily Telegraph of Britain that she met Anders Behring Breivik on an online dating site in 2005.
Her image of him as a "handsome, well-dressed Norwegian" changed not long after she arrived to stay at Breivik's Oslo flat.
"I did not notice that he was planning something so cruel, I knew only that he never respected me," she said.
A Norwegian newspaper said Breivik told his friends that she was after his money.
"I was not a golddigger," Natascha said. "I wanted to see if we could make the relationship work. But we did not communicate well and there was no chemistry."
On Friday a Norwegian court ordered a new psychiatric evaluation for Breivik after an earlier evaluation found him legally insane.
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