Lily Allen has marked 18 months of sobriety.

Lily Allen (c) Instagram

Lily Allen (c) Instagram

The 35-year-old singer took to social media to mark the momentous anniversary having been candid about her drug and alcohol addiction struggles in the past.

In an Instagram post, Lily shared a picture of herself with a key ring given out by support group Narcotics Anonymous to mark the significant date. The key ring read: "Clean and serene for eighteen months."

Lily captioned the post: "18 months clean and sober today. Would recommend!"

Lily recently explained that she knew that she had to go to rehab when she considered taking heroin when she supported Miley Cyrus on her 'Bangerz Tour' in 2014.

The 'Smile' hitmaker – who shares children Ethel, nine, and Marnie, eight with ex-husband Sam Cooper – admits that the "highly sexualised" shows made her feel less attractive as a new mother and after using a diet pill to lose weight she then ended up abusing alcohol and drugs in a destructive way.

Lily said: "I ended up on tour in America supporting Miley Cyrus and it was a highly sexualised tour and I’d spent the last three years pushing babies out.

"I was supporting this girl who was much younger and more attractive than I felt and I just started acting out in all manner of ways."

The 'Smile' hitmaker continued: "I started cheating on my husband and I had always drunk alcohol to take the edge off the drugs.

"Then I realised I was going into the mini bar and drinking the mini bottles of vodka and without the drugs.

"I was in LA and thinking, 'None of this acting out is working anymore. Maybe I should try heroin.'

"But because I had seen what happens to people who have taken heroin I knew it was time to confront whatever it was and my demons."