In the latest bombshell to rock MATT LAUER’s train-wreck marriage, the love rat has secretly carried on a too-close-for-comfort friendship with his morning TV rival, “Good Morning America” co-anchor Lara Spencer!

The notorious “Today” womanizer, 57, was even busted by wife Annette for flirting up a storm with the leggy 45-year-old blonde, multiple sources told The National ENQUIRER.

Lara once accidentally dialed Matt from her cellphone, a well-placed insider revealed, and Annette took the call!

“Annette to this day probably doesn’t know that it was Lara on the other end of the phone,” said the source.

“Lara was at an event when it occurred. She didn’t realize the button had been pressed. It called Matt, and Annette answered. When Lara realized her phone had initiated the call, she put it up to her ear and heard a woman saying, ‘Hello, hello.’ “Frantically, Lara hung up!”

Lara has been wed to former CNN journalist David Haffenreffer since 2000, and they have two kids together.

But that hasn’t deterred skirt-chasing Matt, sources said!

“Lara’s marriage has not stopped Matt lusting after her,” dished one insider.

What’s more, Annette, 49, has “always suspected Matt has a crush on Lara” because of their flirtatious relationship.

“Matt just lights up whenever Lara is around, and they seem to share a lot of laughs,” said another source.

“Annette will go out of her way to avoid Lara on the social circuit, but she keeps her eye on Matt – for obvious reasons.”

And at an event in the Hamptons, the Dutch-born former model was “openly angry at Lara for blatantly flirting with Matt,” a source divulged.

For Annette, revelations about the extent of Matt’s relationship with Lara could be the final nail in the coffin of her 16-year marriage.

She once described Matt in court papers as making her feel “abandoned, isolated and alone in raising” their children.

It’s also a bitter betrayal to Matt’s struggling “Today” show and his beleaguered colleagues who have lost their top-rated position to “GMA.”

The strain on his marriage was apparent when a monster winter storm hit New York City in January, and the “Today” cast was instructed to camp out at the Four Seasons so they could walk to work, revealed an industry insider, who said: “Annette wasn’t happy about that, and ordered Matt to stay in their apartment.

“If he had to walk extra blocks in the cold, she didn’t care! There was no way Annette was going to have Matt staying in the same hotel as co-host Natalie Morales.”

In 2006, while pregnant with their third child, Annette filed for divorce amid talk that Matt was involved with Natalie.

She later withdrew the papers. For now, Annette’s family is seriously concerned about her, The ENQUIRER has learned.

According to family friend Nils Fonteijn, Matt’s in-laws remain “deeply upset at the continuing strife in Annette’s marriage, and her mother is frantic with worry.”

Nils, a pal of Annette’s stepdad, Dr. Dick Struijk, for over 30 years, told The ENQUIRER that they “suspect he [Matt] could be fooling around again,” adding: “Dr. Struijk, who doesn’t often use vulgarities, told me, ‘His [Matt’s] brain is in his d–k!’”