Katie Couric’s two-year romance with millionaire boyfriend Tom Werner blew apart after his estranged wife pitched a fit over Tom’s plans to build an $8-million mansion for Katie.

That’s the real story behind the heartbreaking split between the perky 45-year-old “Today” show star and the 52-year-old Hollywood TV producer.

“The romance just blew up in the beginning of June,” said an insider. “One minute they were hand in hand and the next minute they had split!

“It was shocking. Katie is devastated!”

The romance has been growing for two years, and Tom has been busy planning a massive Los Angeles mansion to share with Katie and her two children.

During the same period Tom has been attempting to work out a divorce agreement with his estranged wife, Jill.

“Tom’s plans for Katie’s posh mansion didn’t sit well with Jill,” said the insider.

“After her split with Tom, Jill was forced to leave her own L.A. mansion this year and move to a 3-bedroom house in Pacific Palisades.

“As a result she has been making life miserable for both Tom and Katie.

“Katie resented that and felt that — after two years — Tom should have the divorce over and done with.”

The issue came to a head when Tom was supposed to be with Katie who had taken a week off from her grueling “Today” show schedule to spend time with him.

“But the two got into a loud fight, and bitter accusations were hurled both ways.

“Katie accused Tom of leading her on and having no real intention of marrying her.

“He accused her of having no sympathy for his situation with an estranged wife. After an angry argument they decided it just wasn’t going to work.”

Katie wound up on her week’s vacation without Tom. Instead, she left town with her children, their nanny and the family dog.

“She was barely recognizable as the Katie Couric we know,” a witness told The ENQUIRER. “She looked sad and forlorn.”

Top Beverly Hills psychiatrist Dr. Carole Lieberman — who has not treated Katie — told The ENQUIRER that Katie, who lost a beloved husband to cancer in 1998, may well be unconsciously sabotaging her new relationship.

“Because his divorce from his wife dragged on and on, Katie may have unconsciously begun to feel insecure about his love. She may have started wondering whether they were ever going to be married — and also what their marriage would be like.

“Katie once had a husband who was definitely devoted to her and to the kids, and she had his full attention and full love.

“When she compares that to having to share the love and attention of this new man, she probably feels at some level that it’s not going to be as good.”