Dad sobs in court as son's injuries are listed.
Yousef Ali Ege, 38, insisted he knew nothing about the child being hurt and denied he had loved his wife so much that he turned a blind eye to her beating seven-year-old Yaseen.
He was being questioned at Cardiff Crown Court, where his wife denies murder and he denies failing to protect their son, when the judge, Mr Justice Royce, ordered an adjournment for him to compose himself.
Ege had sat down in the witness box with his head in his hands after telling the QC repeatedly: "Sir, I did not know anything about these injuries."
Sara Ege, 32, is accused of repeatedly beating their son, eventually causing fatal abdominal injuries in July 2010. She initially confessed to causing injuries Yaseen was discovered to have suffered before his body was pulled out of a blaze at the family home in Severn Road, Canton, Cardiff.
But she later accused her husband of attacking the child and said he forced her to take the blame.
Yousef Ege told the jury: "I never touched him" and Peter Murphy, defending Mrs Ege, beginning his cross examination, said: "I am not suggesting you were responsible for the injuries on July 12 or before (when he had suffered fractures to a wrist, finger and four ribs).
The purpose of my questions is to consider your position if the jury is satisfied that Yaseen died through an unlawful act by his mother." Ege agreed when it was put to him by Mr Murphy: "You loved your wife very much and thought she was a good and special wife, didn't you? But it was your duty to protect your son no matter how much you loved her."
Listing the catalogue of injuries, he asked how Ege could not have noticed, as school teachers had, that the primary school pupil was "in obvious pain", was "having difficulty sitting down" and was "walking like an old man".
Ege said: "Sara looked after him from day one and I was always in work. She.... the teachers.... no-one told me. Yaseen never complained he was in pain. "I thought my son died in the fire. I knew nothing until I was in the police station."
Mr Murphy alleged: "You knew and tolerated it through love and loyalty to her."
"That is totally wrong. I loved my son to bits," Ege told him.
The case continues.