Matt Lauer’s been hiding another secret blow-up in his “train wreck” of a marriage!

In a bombshell new exclusive, The National ENQUIRER has learned the skirt-chasing “Today” show host “walked out” on his long-suffering wife, Annette Roque, this past summer before once again “begging her back for the sake of their three kids,” according to a close source.

The insider said a “bitter fight” sparked their latest split – occurring after The ENQUIRER published photos of the notorious womanizer relaxing on a boat with a mystery blonde in the Hamptons on July 8.

A few weeks later, in early August, Lauer – who turns 57 on Dec. 30 – was living alone at the family’s Manhattan apartment while Annette, 49, and their children stayed on Long Island.

Another source said: “This caused a tremendous new strain in their marriage. Annette felt abandoned again.”

Matt was able to “patch things up” by the early fall, and the couple managed to celebrate a “loveless” 16th wedding anniversary on Oct. 3.

“It’s a train wreck of a marriage and there’s no telling when it’ll blow again!” the insider said.

For the full story with All the details you won’t find anywhere else – it’s ONLY in the new ENQUIRER – on sale now!