The parents of Madeleine McCann have vowed to challenge the Portugese courts’ decision to clear a retired detective of breaching the country’s libel laws.
In an interview with the BBC, Kate and Gerry McCann were asked if they would continue to fight Goncalo Amaral over claims he made in his 2008 book about their daughter’s disappearance.
The McCanns expressed disappointment in February after learning that Portugal's highest court had thrown out their libel claim against Mr Amaral.
He also took part in a Portuguese television documentary claiming Madeleine was dead, there had been no abduction and her body had been hidden.
Mr Amaral was initially ordered to pay the McCanns 250,000 euros (£209,000) each in damages in 2015 over claims made in The Truth Of The Lie after a court banned further sales of the book.
But Portugal's Supreme Court ruled against the libel action, saying claims made in his book are protected by freedom of expression laws.
During the interview conducted ahead of Wednesday's 10th anniversary of Madeleine's disappearance, BBC presenter Fiona Bruce asked the McCanns: "One of the police officers in Portugal has been a thorn in your side for many years, he was thrown off the investigation but then he wrote a book ... and you fought it through the courts.
"At the moment you've lost and he's won. Is this the end for you now, are you going to continue to fight him?"
Mr McCann replied: "I think the short answer is we have to because the last judgment I think is terrible.
"I think it's also important to say that when we lodged the action was eight years ago, and the circumstances were very different, where we felt there was real damage being done to the search for Madeleine at that time, particularly in Portugal."
Mr McCann added that it was important to challenge Mr Amaral in the European courts on behalf of the wider family, including his children.
Agreeing that Mr Amaral's claims needed to be challenged, Mrs McCann said: "I find it all incomprehensible to be honest
"It has been very upsetting, and it has caused a lot of frustration and anger which is a real negative emotion."