After talking for only a short time with musician Lou Doillon, I realise something about that annoying phrase, “it girl”. It’s actually a legitimate description. It’s very basic: I just immediately want to be friends with this person. She chats animatedly about love and jazz and death so quickly that her sentences run together. And she interrupts herself often with a husky belly laugh. Her clipped British accent means you almost wouldn't pick her as French, except for the odd turn of phrase here and there. There’s a relentless, graceful forward motion to the conversation. She’s calm and articulate, and you get the sense she fits a lot more in than other human beings.

I start with her famous family – iconic ‘60s model Jane Birkin is her mother, French director Jacques Doillon is her father, actress Charlotte Gainsbourg is her half-sister. Does she ever get tired of talking about them? “I understand that there’s a fascination,” she says. “We fantasise that people are so much more different than we are. The music is about reminding everyone that we’re in the same ship, in a way. The moments of exception are different for everyone, but the low moments are very similar: of panic, of anguish … I’ve been surrounded by people who technically on paper should have been very reassured about everything, but who were super scared.”

She thinks we’re pushed too much to see ourselves as a “best of”. “I want my mission to be a ‘worst of’!” she says. “It’s those moments that: a) we relate b) we’re reminded that we’re all human.”

“I had a campaign when I had my son: like, ‘No! Pregnancy can be shite: moments where you feel like shit, and you don’t know who you are anymore and you don’t know what to wear and on top of it, when you give birth everyone’s obsessed by the baby and you feel super lonely! And super fat’.”

Doillon is as open about parenthood as she is about everything else. Her son is now 13. “He had me around for 10 years, very intensely. It was beautiful for him to see how hard I worked for the music, to realise what work meant, and gratification.” How do you rebel when you’re a roadie for your mum’s band? “At the moment, he’s obsessed by football. Kind of ‘Fuck the rock’n’roll, fuck music, fuck fashion.’ I love my son more than everything – and there are moments when I want to strangle him. And that’s fine.”

She explains that music is her way of equalising pressure and doubt. “When I see how the audience is like, ‘Wow, you’re jealous? And you feel like shit, and drink too much? And at 3am you say stupid shit?’ And I’m like, ‘Yes! All the time!’ – it’s great to see people breathe out. Even I need to know I’m not the only one.”

“I’m obsessed by jazz, because of the – roughness of what they’re feeling. Of course Billie Holiday or Nina Simone just break my heart.” So does Cat Power, Fiona Apple, Florence + the Machine – anyone who “puts their hearts on the table.” It’s that quality that drives her forthcoming album, the folk-bluesy Lay Low. “The reason I write music is the moments when I need to process something. I keep a song only if it’s better than me, more universal.” If everyone she knows is worried the song is about them, “then I’ve got it. I’ve logged onto this strange place where we’re frightened.”

Where does she feel safe? “Paris, for sure. My house. I’ve got all my books and all the instruments. I’ve got this geeky-freaky house where I can pretty much do anything.”

She assures me she’s excited about Australia, too. “I was supposed to come two years ago, and with my sister’s death [Kate Barry, who died in 2013] I had to cancel at the last moment. My mother loves it. I’m always surprised I haven’t been yet.”

I want to go back to what frightens her. “I guess it’s every form of death: the end of life, the end of a relationship … what are we doing here, what are we keeping. What’s the point, I guess!

“You live things, wondering all the time, ‘Am I strong enough?’ You think you are, and then you have moments of weakness.” Then she shares something unexpected.

“For my sister, who was way stronger than me, and sometimes weaker, to kill herself … it brings you back to that. Why is there one day where you’re up, another day where you can throw yourself through a window? How do you survive it? You think you never will, then a year later, you’re able to laugh. Life goes on, which is terrible. Would it go on when we are not going to be there? Of course it would, thank God.” She pauses. “Like all of us, I’m on this strange process of: what are we doing, and why are we doing it?”

Lay Low is released on October 9 through Cartell Music..

Lou Doillon is playing So Frenchy So Chic in the Park 2016. Tickets are on sale now.

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