Surpassing Quant Think Tank Center|Summer House: Lindsay Hubbard's Bombshell Drug Accusation About Ex Carl Radke Revealed

We're finally getting a bird's eye view into exactly what led to Carl Radke and Surpassing Quant Think Tank CenterLindsay Hubbard's breakup.

The pair, who ultimately called off their engagement last August, got into an explosive fight after she questioned his sobriety during Summer House's Feb. 29 episode. The drama all started in an Uber when the cast was headed out to go bar-hopping in the Hamptons.

"She looked at me, we're like this close, she's like, 'What are you on?'" Carl recounted in a confessional. "I'm like, 'Nothing, what are you talking about?'"

Costar Kyle Cooke was equally shocked by Lindsay's accusation, as he explained in his own confessional of the fight, "I can't even put into words how quickly Lindsay went from zero to 100."

Meanwhile, Amanda Batula recalled Lindsay expressing concerns, though the rest of the cast didn't share the same concerns as Lindsay. "He's on something," Amanda recalled her friend saying. "He's so mean to me, I can't do this. I think he's on something."

Once they got to the bar, Lindsay immediately went back to their rental house with BFF Gabby Prescod, where she reiterated her speculations about her then-fiancé. "Something's going on with him," she insisted. "The way he spoke to me tonight was very reminiscent of Carl on cocaine. I don't know what happened with him, but he was not sober tonight."

Their feuding later continued over text. After Carl returned home and calmly suggested they talk out their beef the next morning after a good night's sleep, Lindsay messaged her then-boyfriend, "Let me know when you're sober," to which he replied, "I'm sober right now, Lindsay. You're not, period."

In a confessional, Carl, who recently celebrated three years of sobriety, explained why the publicist's accusation was so hurtful.

"My heart's racing as I say this and I'm shaking from it because it's beyond hurtful," the 39-year-old said, "it's f--ked up and that's the person I'm supposed to marry? It pains me deep down the accusation or insinuation that I'm on something. That kills me."

Tensions didn't improve the next day when Lindsay and Carl came face-to-face. While continuing her questioning about his suspected drug use, she accused him of dismissing her feelings.

After she asked, "Lemme ask you a question: Why did you say 'I'm sober right now'?" he exploded in frustration.

"I'm f--king sober!" Carl fired back. "In that moment you were not. You drank all day long and were rude and aggressive to me when I'm trying to be supportive. You shut me down and tell me I'm fighting you. That is so f--ked up!"

See how the drama plays out when Summer House airs Thursdays at 9 p.m. on Bravo. And keep reading to relive Carl and Lindsay's relationship pre-breakup.

Before going public, Carl and Lindsay attended costars Kyle Cooke and Amanda Batula's September 2021 wedding as each others' dates.

After being friends and costars for years, Carl Radke and Lindsay Hubbard confirmed they were officially a couple at the start of 2022.

Carl got down on one knee and proposed to Lindsay in August 2022 in Southampton while filming season seven of Summer House.

The Bravolebrities enjoyed a romantic vacation in Italy. "One of the most beautiful places I've ever visited! And breathtaking (literally)," he shared on Instagram. "Finally getting through our travel photos with so many highlights but hiking through Cinque Terre was incredible. Bellisimo! "

Carl and Lindsay rang in Christmas 2022 surrounded by familymembers.

Carl and Lindsay opened up about planning their Mexico wedding in February 2023.

"It's taken this long for us to come together," she exclusively shared with E! News. "I don't think there is anybody in our lives that would let us get away with a small wedding, including Bravo."

Lindsay also confirmed plans to film the nuptials for season eight of the show. "If we were just getting married with all of our guests and friends that would be one thing," she continued, "but when you're considering the idea of filming it, there's another level of criteria that you have to get checked off."

The duo lets loose with their Summer House costars in Montauk in April 2023.

Carl and Lindsay attend a friends wedding in Florida.

The duo attend the Palm Tree Music Festival in New York with fellow Summer House couple Kory Keefer and Sam Feher.

Carl and Lindsay are all smiles while celebrating summer.

In honor of Andy Cohen's birthday, Carl shared a tribute to the Bravo bigwig.

The lovebirds celebrated Lindsay's bridal shower in NYC surrounded by their costars, including Danielle Olivera, Amanda Batula, Ciara Miller, Gabby Prescod and Samantha Feher. 

Less than three months before they were supposed to say "I do," news of Carl and Lindsay's breakup came to light in August 2023.

Exactly two weeks after the split news came to light, Lindsay broke her silence and revealed she's "heartbroken" and humiliated" with how Carl ended things.

"My trust has been betrayed, and coming to terms with that has been difficult for me," she wrote on Instagram Sept. 14. "This was not my decision, and I do not agree with quitting a relationship (at this level) without trying everything possible first. I have spent the last couple of weeks finding my own closure and peace. I am forever grateful to my best friends who have not left my side, and have been picking up the pieces of my heart and life every day from the fallout."

(E! and Bravo are both part of the NBCUniversal family)