The singer, 33, took to social media to play a short clip of the track – admitting the move might get her in trouble with her management.
On Tuesday, Adele took to Twitter to confirm the track – her first in several years – is set for release on 15 October.
During her live stream, she said she was feeling “very good” currently in terms of her mental health, but took things “day-by-day”.
“My mental health is very good at the moment. I take it day-by-day and I address whatever comes my way.
“It definitely helps me feel better if I take my time. Writing my music… yeah it’s been really therapeutic for sure.
“I think I lost the appreciation for that. I got things out that I didn’t want to say out loud and talk about.”
Fans went into meltdown at the shock appearance – with a number asking questions about her upcoming release.
Answering one question about what her upcoming album is about, Adele answered: “What’s my next album going to be based on? Divorce, babe, divorce.”
Adele split from her ex-husband – charity boss Simon Konecki – in April 2019.
Their divorce was finalised in March this year. They share custody of their son Angelo.
As well as confirming she was releasing new music earlier this week, Adele starred in the covers of both US and British Vogue.
It was the first collaboration of its kind in Vogue’s 129-year history, with each edition of the magazine featuring a different fashion shoot and interview.
In the interview she revealed that a lot of her upcoming album has been recorded for her eight-year-old son.
“I just felt like I wanted to explain to him, though this record, when he’s in his 20s or 30s, who I am and why I voluntarily chose to dismantle his entire life in the pursuit of my own happiness,” she said.
“It made him really unhappy sometimes. And that’s a real wound for me that I don’t know if I’ll ever be able to heal.”
The singer also spoke about her significant weight loss in the magazine.
She said: “It was because of my anxiety. Working out, I would just feel better.
“It was never about losing weight, it was always about becoming strong and giving myself as much time every day without my phone.
“I got quite addicted to it. I work out two or three times a day.”
Adele has not released an album since 2015’s 25 but she has confirmed she is working on a new record.
All three of her studio albums so far have been named after the milestone ages she hit during the creative process.