Lena Dunham just made a bombshell confession that she cheated on music producer Jack Antonoff during their five-year relationship, whilst she had suspicions about his close relationship with “a teen pop star.”

The actress opened up about her tumultuous relationship with Taylor Swift’s writing partner in her new memoir, Famesick, released on Tuesday.

Dunham wrote that she and Antonoff had their “worst-ever fight” after her hysterectomy surgery in November 2017, which resulted in a rehab stint for her addiction to post-surgery pain medication.

She and Antonoff then paused their relationship as she went on tour.

Lena explained that during this time she ended up reconnecting with a childhood friend and ex named Nick, but admitted she should have been paying closer attention to Antonoff, who had been spending extended time in the studio with a “teen pop star.”

For years, rumors had been swirling that Antonoff was involved romantically with Lorde, but the two have always denied that they have had any romantic relationship going on.

Dunham wrote how “up until now, I had seen myself as some kind of half wife, and so I had observed wifely code but the events of the past few weeks had changed the game, and it was every woman for herself, just trying to survive.”

Things escalated as the actress went on a date and took a cab back to Nick’s apartment, where she wrote that she told Nick, “I’ve been through something awful. I don’t want to talk about it, but I need you to f*** me and I need you to do all the work.”

The two continued sleeping together for two weeks while Antonoff was on tour and they even got “engaged” after her split from the musician but ultimately ended up breaking up after Dunham’s rehab stint in 2018.

Dunham also addressed infidelity rumors from Antonoff’s side, revealing that her partner had been spending time in the studio with a “teen pop star” whose name she did not reveal.

She even wrote that the star was “weeping into Jack’s lap” when she came home one day.

The Sharp Stick actress explained that whilst she “flirted” with others during their relationship “I had observed careful boundaries, never taking it far enough that I could be declared out of bounds.”

“If I’d wanted to look, perhaps I may have seen that Jack was not observing them as closely as I was. I wasn’t paying attention, but the internet sure was, and they made some pretty amazing PowerPoints on the issue, so convincing they had me rethinking events that I myself had been present for,” Lena Dunham mentioned of how she started doubting Jack Antonoff of infidelity.