JOE O'Reilly told his lover to tell gardai their relationship was not serious as it could provide a motive for his wife's murder.
And the murder accused spent the night with his lover - Nikki Pelley - after he made a public appeal on RTE's Late Late Show for information about Rachel O'Reilly's murder.
Despite telling gardai their affair was 'over', he stayed at Ms Pelley's Rathfarnham home just over two weeks after his wife Rachel's battered body was found at the home they shared in north Co Dublin.
Ms Pelley, who took the stand at his murder trial yesterday, said that Joe O'Reilly told her to tell gardai their relationship was merely an 'affair' because if it was serious it would provide a motive for his wife's death.
Despite the couple having discussed a future together, Ms Pelley told gardai their relationship was just an affair when questioned after the discovery of Rachel's body on October 4, 2004.
And it emerged that Ms Pelley had stayed in the O'Reilly family home in The Naul, and that Joe told her Rachel and he had 'effectively separated' and slept in separate bedrooms.
He also referred to his wife as a 'wasp' and a 'c***' to his lover.
Ms Pelley began giving her evidence yesterday on the 14th day of the murder trail.
Joe O'Reilly (35) of Lambay View, Baldarragh, The Naul, Co Dublin, is accused of murdering his wife Rachel at the home they shared on October 4 2004. He denies the charge.
Yesterday Ms Pelley, who lived on Ballyroan Road in Rathfarnham, told the court she used to work with the accused and met him at a function in the Barge pub in Portobello in January 2004.
After the function, they began exchanging text messages and emails and later started meeting for lunch in the Templelogue Inn a 'month or a couple of months' after The Barge function.
After going on a date to the cinema in Liffey Valley, they began a sexual relationship.
"I used to meet him at lunchtime and started a sexual relationship with him in April or May in 2004," she told the Central Criminal Court. They would meet three of four times a week, 'mainly in my house', and Mr O'Reilly would sometimes stay at her home on a Tuesday and Saturday when they would meet to have sex.
Asked if Rachel knew of the affair, she said she didn't think so, adding she had only seen her 'once' at a softball tournament.
"I'd see him on Saturday afternoons, and he would tell Rachel he was staying in the office," Ms Pelley said. And she revealed she had stayed in the O'Reilly home in The Naul.
"We went down to our family home in Wexford for a couple of days," she said. "He had told me they had effectively separated a year and a half before we met, they had separate bedrooms." She met his children Adam and Luke, and was introduced as Nikki. She also stayed in The Naul on one occasion when Rachel was 'down the country'. After the murder, Ms Pelley was interviewed twice by gardai on October 5 and October 27. She was also arrested on November 16 in connection with the case.
Asked if she told gardai the 'truth' about their relationship, she replied: "No. I told them it was just an affair. He (Joe O'Reilly) just suggested it was an affair and asked me to do the same."
"Did Mr O'Reilly ever discuss the future," prosecution counsel Dennis Vaughan Buckley asked.
"We talked about things, about a future, about being together," she replied.
"There were two options - the children would stay with Joe or with Rachel."
She was also asked by prosecution counsel Denis Vaughan Buckley SC why she did not reveal the true extent of their relationship to gardai.
"I don't know why", she said.
The trial continues today.