Supermodel ex of Leonardo DiCaprio, Nina Agdal, was caught straddling new boyfriend Jack Brinkley-Cook at Long Island hotspot, Montauk. And when they were caught, they allegedly flipped out.

“They were then escorted to a VIP area and she jumped on top of him and started straddling him,” a source said to Page Six. “They were dry humping, making out, and he had his hand up her shirt. They were really going at it . . . She was bouncing up and down in his lap.”

The guest started taking pics, and Nina wasn’t ok with it. “She said, ‘Let me see your phone! Give me your phone,’ ” said the guest “She was saying, ‘You’ve got to delete those!’ ”

As Page Six reported: The source added Brinkley-Cook “came over and said, ‘What the f - - k?! Let’s go, right now!’ ” He apparently added, “I’m gonna beat the s - - t out of you!” The source said that a group of Brinkley-Cook’s pals then began chiming in. When the guest refused to delete the pics and headed to the lobby, he said Agdal “was in tears. She was saying, ‘We were supposed to be at a wedding tonight,’ ” (and the hosts would learn they were instead at Gurney’s). The fotog agreed to erase the shots . . . if Brinkley-Cook apologized. Instead, Brinkley-Cook allegedly exclaimed, “F - - k that!”