Murder accused Kieran Greene had no other girlfriends before he met Patricia O'Connor's daughter Louise, a Central Criminal Court jury has heard.
Mr Greene's mother Joan also said her son had seemed "tired and withdrawn" when she visited him in prison since he was arrested. She was the only witness for the defence as evidence concluded in the joint trials of four people over the death of Patricia O'Connor (61) in 2017.
One of the charges against a co-accused, Keith Johnston (43), was withdrawn from the jury. Mr Justice Paul McDermott withdrew a charge that he refurbished the grandmother-of-seven's bathroom to destroy or conceal evidence of her murder.
Mr Johnston faces a remaining count alleging he helped Mr Greene to buy tools for use in concealing Ms O'Connor's remains.
Mr Greene (35) is accused of murder, while Patricia's daughter and granddaughter Louise (41) and Stephanie O'Connor (22), as well as Mr Johnston, are charged with impeding his prosecution. They have all pleaded not guilty.
Patricia O'Connor was allegedly murdered on May 29, 2017, at the house at Mountain View Park, Rathfarnham, Dublin, she shared with family including Louise, Stephanie and Mr Greene. Mr Greene was Louise's partner at the time, while Mr Johnston, Stephanie's father, was Louise's ex-boyfriend.
Ms O'Connor's dismembered remains were found scattered in the Wicklow mountains. She died from blunt force trauma to the head.
Joan Greene said her son was assessed in primary school and he was about two-and-a-half years behind. He got extra tutoring. She said Mr Greene lived at home until he met Louise O'Connor and had no previous relationships as far as she knew.
Ms Greene and her husband had agreed to act as guardians to the three children of her son and Louise O'Connor and signed a consent document on September 15, 2017.
It was at Louise's request after her arrest, as she was concerned for the future of her children. The trial continues.