Every girl knows that you don't, under any circumstances, date your best friend's ex. Clearly, Lorde never got that memo, according to romance rumors.

Lena Dunham thought Antonoff was going to propose

Back in November, lena dunham admitted that she mistakenly assumed that her then-boyfriend was going to propose to her.

She had overheard a conversation between him and his sister and had heard the words "Lena" and "finger." Which makes sense as to why she would have thought they were talking about him proposing to her.

It turns out that Dunham had actually caught Antonoff [VIDEO] and his sister talking badly about her.

To shake off the embarrassment, Lena tweeted to her millions of followers that she was laughing her head off and was keeping Jack awake because of it.

She then went on to talking about how she wants Cardi B's ring.

As for Jack, he certainly wasn't amused as he broke up with the 31-year-old actress just a month later.

Is there a romance between Lorde and Jack Antonoff?

Rumors are certainly saying so, and there is just a little bit of proof to prove that theory.

According to an insider with US Weekly, Jack Antonoff has already moved on and is reportedly seeing someone else. Could he be keeping it low key because that "someone" is Lena Dunham's best friend, Lorde?

The Bleachers lead singer worked with Lorde on her most recent album, Melodrama. When the album released, Dunham posted a photo to her Instagram celebrating the release. In the caption, she mentioned that Ella, Lorde's birth name, and Jack had recorded most of the album in her and Jack's apartment.

The caption also mentioned that Lena had fun watching them create music and feeding Lorde little snacks.

After the breakup, fans noticed that Dunham had deleted that photo from her Instagram page.

Although it is unclear as to when she deleted that photo - and as to why - naturally, fans are ultimately speculating that it has to do with the rumors that Lorde is now dating Dunham's ex-boyfriend. Or maybe she just wanted every photo of Jack off of her Instagram feed. But why would she delete a photo if it had her close friend in it as well?

Aside from helping the New Zealand singer record her album, he is also credited with almost every song on the album.

Antonoff also frequently works with their mutual friend, Taylor Swift, who Lena Dunham also used to be quite close with.

So the question is, did Lorde "steal" the young actresses boyfriend? Although the proof is there and quite telling, we'll never know until Lorde or Lena confirm it themselves. Let's just hope that in the case that it is true, that Lorde is ready for the backlash she'll receive for breaking "girl code."