Lena Dunham ''made out'' with a guest star on 'Girls'.

The 30-year-old actor - who is now in a relationship with musician Jack Antonoff - was single during the first season of the show and admitted she crossed the ''boundaries of professionalism'' with an unnamed actor.

She confessed: ''I did make out with a day player actor on our show in the first season. Before we understood the full boundaries of professionalism.

''I was like, 'You've been on set for eight hours. You seem interested in me and my power. I would love to go to the 11th Street Bar with you.' ''

However, Lena quickly realised meeting up with her co-star outside of filming wasn't a good idea and felt she was acting like ''the grossest male producer''.

Speaking with some of her castmates at the TimesTalks: A Final Farewell to the Cast of 'Girls' event, she continued: ''Then I kind of got there, I was like, 'Oh wow, this person doesn't even think I'm cute.' He's just like, 'She runs a TV show and I'm actor.' I was like, 'This is a nightmare. I've inadvertently become the grossest male producer.'''

And her realisation made Lena resolve that she wanted to ''commit to the same person for the rest of [her] life'' afterwards.

Also during the discussion, Lena shared her hope that 'Girls' has depicted female friendships accurately and taught women that it is OK to be flawed.

She said: ''I hope that it helps people think of women as messy and complicated, containing multitudes.

''That it's OK for women to be unsure and impolite... One of the big goals when we started the show was to really talk about female friendship in a really honest way, because in so many films we see, they're depicted as they're depicted as this sort of 'ride or die,' support of perfection, or catty fighting.

''The truth of female friendship is that it's a really deep love that lies between those things.''