LONDON - British actor Colin Firth's wife has admitted an affair with an Italian journalist she has accused of stalking her.

Firth, 57, and his wife of 20 years, Italian film producer Livia Giuggioli, 48, filed a complaint against Marco Brancaccia last week, said The Times, citing Italian reports.

The couple confirmed the affair in a statement issued to the media.

"A few years ago Colin and Livia privately made the decision to separate," the statement read. "During that time, Livia briefly became involved with former friend Mr Brancaccia. The Firths have since reunited. Subsequently, Mr Brancaccia carried out a frightening campaign of harassment over several months, much of which is documented."

According to their complaint, Brancaccia made threatening phone calls, e-mailed photos of Giuggioli to her husband, and threatened to write articles about them at ANSA, the Italian news agency where he works, said Vanity Fair magazine.

The Italian police have seized his phone and computer, and an investigation is underway.

Brancaccia, 55, has denied stalking Giuggioli. He told The Times she made up the claims to cover up the relationship they had between 2015 and 2016.

"We were romantically involved, she wanted to leave Colin for me," he told the British newspaper. "My 'stalking' consisted of two messages via WhatsApp after she ended our relationship in June 2016, and an email."

He added: "I wrote an email to Colin about my relationship with Livia, which I now regret sending, and she filed a complaint against me for stalking out of fear that I could go public with what she had revealed to me about her marriage and work. In a year she sent me hundreds of messages of love, photos and videos, even a diary."

Firth and Giuggioli have two sons. The actor has another son from a past relationship with Canadian-American actress Meg Tilly.