Wife discovered all at once that her husband of 23 years had a secret fiancée and was also accused of the woman's murder

Melanie Addie and her ex-husband James were married for more than 20 years and had two children together, a daughter named Emma and a son named Ben. While their marriage wasn't perfect, nothing appeared overtly out of place, and Melanie had no inkling that James was living a double life.

But then one night roughly three years ago, everything changed. Police showed up at Addie's front door to report a death. Before long, she realized that her husband had been having a secret affair with a woman for seven years whom he planned to marry — and whom he was now accused of murdering.

In an interview with ABC's "20/20" set to air Friday night, Melanie Addie opened up for the first time outside of court about her doomed marriage and the moment she learned about her ex-husband's fatal affair.

"It was just mind-boggling. It made no sense at all," Melanie recalled to ABC. "It didn't seem right. This was not my life."

James Addie, 56, was sentenced to life in prison without parole in 2021 for the murder of his fiancée, 35-year-old Molly Watson, only days before their wedding day. Watson was discovered outside of her car on a rural road in Monroe County, Missouri, with a gunshot wound to the back of her head. She was wearing her engagement ring at the time of her death.

Though shocked to learn of her ex-husband's criminal behavior, Melanie later came to believe that James was, in fact, capable of the heinous act.

"He was a pretty selfish person ... He could be controlling and intimidating... it could be challenging," she said. "It just seemed like something he would do to fix a problem."

Melanie reportedly maintained that she didn't suspect that James was having an affair and thought he was dedicated to their family. But a few weeks after his arrest, she filed for divorce. And that's when she started examining their marriage and realizing some of the inconsistencies.

"He seemed the same all the time," she recalled. But she noted: "He would get off work at 3 [p.m.] ... and usually he would get home at 5 and I would say, 'Why are you always so late?' ... and that would be an argument. He didn't want to tell me anything."

Sometimes, Melanie added, her ex-husband would go off on trips supposedly with colleagues or friends.

At one point, Melanie started rummaging through the garage — where James spent a lot of time — and discovered a photo album in a locked chest that showcased details of his double life, including pictures of him and Watson in Florida together.

During sentencing, James Addie read a love letter to Watson and asked for a new trial. He claimed his defense attorney was ineffective and failed to adequately defend his innocence, ABC News reported.

"There is no way that I could have done this crime," he said in an address to the court. "The only one I hold at fault in this entire process is my attorney because he had the means and he had the ability to present my case and he failed to do it whenever I asked him."

"I got myself into something I shouldn't have." | COURT TVwww.youtube.com