Brody Jenner's GF Sparks Major Drama on The Hills with Kaitlynn, Audrina & Heidi

Brody Jenner's decision to bring "friend" Amber with him for a cast trip to San Diego on "The Hills: New Beginnings" backfired big time on Wednesday night's new episode.

While Kaitlynn Carter said she and Brody were "in a really good place" at the top of the hour, his choice to invite Amber along for the ride without telling anyone else definitely rocked the boat for the exes.

"I 100% would have let Brody know if I was bringing a date on this trip. Like a heads up, I just think would have been thoughtful," Carter said in a confessional. "It takes 30 seconds out of your day to just send me a text. I know Amber. We were all friends in the past and I'm just surprised, especially with Brody wanting to be sober right now, that if he was starting to date someone more seriously that he would date a girl who I think in general is kind of a partier."

Audrina Patridge -- who had her own recent fling with Brody -- was also "in shock" that he brought a guest when they arrived in San Diego. She flat out asked him if Amber was his girlfriend, prompting an awkward, "Girl thing" response from the duo, who have been keeping things casual.

It was a bit uncomfortable for Amber later when, during a group dinner aboard a boat, Brody and Kaitlynn started talking about some of their more memorable dates. At one point, Amber even commented -- under her breath -- that she was "over this conversation."

"Don't think you can expect to go on a trip with your boyfriend's ex and not have there be funny stories that come up," Carter said in a confessional. "Are we not supposed to talk about anything because Amber's there?"

Justin Bobby pulled Kaitlynn aside for a little chat as two of the few single people on the getaway, where Carter said she "wasn't expecting this to be a couple's trip." She also told him she feels like Brody "can't be by himself for a couple days" and didn't understand what the "deal" was between him and Amber.

The next day, Carter actually confronted Brody about everything and let him know how the situation really made her feel. In a confessional, she also said she felt like his decision to keep her out of the loop negated the trust they had formed since their split, adding, "I really feel kind of foolish."

"I didn't think you would bring somebody. I was surprised, I didn't know," she told Jenner, who said it was a "last minute" decision. "Not that I care if it is or isn't, but I guess I would have expected if you were going to bring somebody on this trip, it would mean it was more serious," she added.

"I hope it didn't make you uncomfortable, that wasn't my intention," he told her. "It's bound to happen at some point. We haven't been together for over a year and a half."

She replied by simply saying that if the roles were reversed, she would have given him a heads up. He said the two were just "having fun" -- with Kaitlynn telling him she was "glad" he was. In a confessional, he admitted to feeling like "the bad guy" for not warning Carter ahead of time, adding that he's trying to be "understanding of her feelings" as part of his personal growth.

Amber was the catalyst for more drama near the end of the hour at another group dinner, where a very drunk Heidi Montag was throwing back tequila shots while encouraging Brody's GF to join in. Amber was worried Brody -- who is on a sober kick -- would get mad at her if she got too tipsy.

"I'm gonna hear it ... Brody's always right," she said, before downing her drink. "I don't want to get crazy, because he'll get mad," she added.

As Audrina hopped around tables, she relayed Amber's feelings to Brody -- telling him, "Apparently, Amber is saying you don't like her drinking. Maybe because you're not drinking, so you don't want her to. But she's 24."

He told Patridge that she had no idea what Amber was like behind closed doors or "what she's like when she's wasted." He added, "You can't come over here and say shit like that when you know nothing ... you don't have to say it's because she's young."

Audrina was taken aback by his response, though he explained himself a little better in a confessional. "Amber and I have our own relationship with her drinking. All I'm doing is watching out for her, because I've been there," he said to camera. "It's not controlling, it's not manipulative, it's none of their business."

Looking for backup, Audrina started calling for Heidi to join their table and tell Jenner what Amber had just told them. Spencer did his best to keep her from going over there -- not wanting 1.) for Heidi to face the wrath Audrina just got and 2.) to fight Brody himself if he spoke to his wife the way he had Patridge.

The episode ended with Heidi getting up, drink in hand, and a preview in which Montag tells Jenner, "She can do whatever she wants. You're not her f---ing dad, her boss." She's also seen shouting, "He's such an a------!"

"The Hills: New Beginnings" airs Wednesdays on MTV.