A former soldier accused of murdering his dying 10-year-old son has been described as a "brilliant father" who was a changed man after the boy died.
Doctors had said Jacob would not live beyond his 20s
Family and friends of Andrew Wragg, 38, told Lewes Crown Court he worshipped Jacob, who had a degenerative disease, and his brother George.
The court heard that despite Jacob's deteriorating condition, he had an "amazing" relationship with him.
Mr Wragg denies murdering Jacob at home in Henty Close, Worthing, West Sussex.
The former SAS soldier admits manslaughter on the grounds of diminished responsibility, claiming he took Jacob's life in a mercy killing on 24 July last year.
As Mr Wragg finished giving evidence on Tuesday, Philip Katz, prosecuting, asked him what he meant by mercy killing.
"I felt it was the best thing that could happen to Jacob and I believe Jacob believed that too," he replied.
Mr Katz also questioned Mr Wragg about whether the boys' mother, Mary, knew about what he intended to do on the night of the killing.
Mr Wragg had claimed earlier he had told his wife that he planned to take Jacob's life, and that she had replied: "Why wait?".
He told the court on Tuesday: "I have put my hands up to taking my son's life. I am not going to start lying about petty things like that."
Andrew Wragg told police his son's death had been a mercy killing
The court also heard from a former girlfriend of Mr Wragg's, Shelley Ansell, who returned from a holiday in Spain to give evidence at the retrial.
"He loved spending time with them (the boys)," she said.
"Jacob doted on his father. Jacob was very affectionate but more to Andy than anyone else. He really was a loving father."
The defendant's brother, Christopher Wragg, said that following Jacob's death, after he was released on bail, his brother became withdrawn.
"Andrew was a different person," he said.
Christina Chandler, the defendant's younger sister, said in a statement: "I know Andy could be difficult to live with but he was brilliant with the kids."
The trial continues.