Mr Millican, who also told Antrim Crown Court, sitting in Belfast of the couple's plans to patch up their marriage, said that he got a phone call around 1.30pm the day of the killing from Pamela Henry, who worked with her in the launderette.
He told the jury: "Pamela was very hysterical, crying and shouting. She said to me: 'Ken, Ken get down here. Freddie's got a gun and he's going to shoot Marion'."
"I said to her: 'Ring the police and I would be straight down".
Mr Millican said he followed closely behind a police car as it travelled at speed to the seaside town.
"I went into the launderette and saw Marion lying directly in front of me, half-way down. I thought she was unconscious and I tried to feel her pulse. There was no pulse," he said.
[...]
Earlier, he told a prosecution lawyer that after 35 years of marriage, they began to have problems, and that Marion eventually moved out of the family home in 2009 following an "amicable split".
In late 2009 he discovered she was in a relationship with Mr McClenaghan.
However, he said late the following year it had ended and they decided to "give our marriage another go".
Mr Millican said that while estranged from his wife, he had noticed a change in her. He also told the court he subsequently learned that Mr McClenaghan had beaten her, once knocking her unconscious.
On another occasion, he claimed Mr McClenaghan had attempted to strangle her, telling her: "You belong to me now and nobody else."