Anne Shortall was not pregnant when she was beaten to death by murder accused Roy Webster, the Central Criminal Court has heard.
When gardaí told Mr Webster this, he replied: "I f***ing knew it."
Detectives put it to him in interview that this had been determined in a post-mortem on Ms Shortall's body.
The jury also heard Mr Webster told gardaí he did not intend to kill Ms Shortall, and hit her with a claw hammer in a "panic reaction" when she threatened to "blow the lid" on their one-night stand.
In the interviews, Mr Webster said he hit Ms Shortall three to four times on the head and felt like he was having an out-of-body experience or "watching a horror movie".
Mr Webster (40), a father of two, from Ashbree, Ashford, Co Wicklow, denies murdering Ms Shortall (47) on April 3, 2015 at the Murrough, also in Wicklow.
He has pleaded guilty to manslaughter, but that plea was not accepted by the prosecution.
Detective Garda Fergus O'Brien said the accused was interviewed, after his arrest, on April 7 and 8. Mr Webster, a cabinet-maker, told gardaí he was on job-seeker's allowance because work had dried up.
He said months after he had sex with Ms Shortall, she told him she was pregnant and an abortion would cost £6,500.
On Friday, April 3, he drove her in his van down to a quiet place called the Murrough. He asked had she a pregnancy test done, and she said she hadn't.
She said "so you don't even have the money with you now" and started shouting, he said.
He told gardaí she got out of the van and said: "Don't you f***ing worry about it, I'll sort it out myself."
He said he got out to reason with her and she started threatening "if I didn't cough up, she was going to start ringing my wife and ringing my house".
"There was a bit of me pleading with her, 'please don't, please don't', I said 'I have a wife and child and a newborn baby at home, please don't ruin that for me'," he told gardaí.
He said she replied: "I don't give a s***." He said his head was spinning and he could "just see my whole world crashing down - this one had my back to the wall".
"I swung open the side door of the van, and I grabbed the first thing, it was a hammer. I hit her on the head with it," he said in his interview.
She fell back into the van, and, still conscious, told him "You f***ing p****, I'll f***ing ruin you", so he hit her again, his statement continued.
He said there was "blood pouring out of her head… I couldn't believe how much".
He told gardaí he taped Ms Shortall's head first as he "thought the tape might stop the blood".
"I also put tape on her hands to stop her flailing around," he said. "I suppose subconsciously I didn't know whether she was dead or alive."
He went home, leaving the body in the van. He "played with the young one, fed the baby", watched TV later and fell asleep on the couch.
"[On Sunday] Anne was still in the van. I thought, Jesus, I am going to have to take her out," he said. He lifted her out and put her in the workshop. For the rest of the day he stayed in and had a "pyjama day", watching movies with his kids.
Asked what he had planned to do with the body, he said: "I had no idea." He was asked why he had brought the body home. He said it was just "natural instinct to come home".
He was asked if he had thought Ms Shortall might have been alive in the back of the van.
"Possibly, yes," he replied. "That is why I put the tape on her hands."
He was asked if it had been his intention to kill her.
"No, not at all," he said.
The gardaí asked what he thought Ms Shortall's reaction was going to be when he told her he had no money. He said: "I didn't know what her reaction might be, I just wanted proof she was pregnant and then I would get her money."
It was put to him that he never intended giving her money and he intended to kill her.
"No, that never crossed my mind," he said. "I am not that type of person, it never crossed my mind, I wasn't brought up that way."
Injuries were read out to the accused, including "left cheek broken" and "nine blows to the head, including the forehead".
"All for nothing, wasn't it Roy?" he was asked.
"Blackmail," he replied.
"Did you kill her because she was pregnant?" he was asked, to which he replied: "No."
"I hit her because she was threatening my family and my livelihood," he said.
"Looking back now, after it was done, I know I was wrong."
He was asked if he went down to a quiet area "to kill her, to shut her up?"
"No, I only went down there to be discreet," he said, adding that his name was on his van.
Mr Webster said if he had been holding Ms Shortall down with one hand and hitting her with a hammer, "surely I would have had scratches on me".
He was told by gardaí Ms Shortall had died of blunt force trauma to the head. "I have heard of that one on 'CSI'," he replied. "So she bled from inside her head."
The trial continues.