The West Lothian chart sensation, who was performing live at the London O2 on Friday (September 2), halted the gig around 10pm to share the new track, which went out simultaneously on his TikTok account.
It comes after the Whitburn superstar teased fans earlier this week that new music could be imminent.
Ahead of tonight’s big announcement, a message on his official website had read: “Lewis Capaldi, Tik Tok, 2nd September, 10pm BST, 2pm PT, 5pm ET.”
It led fans to speculate that the singer may be about to release new music – and so it proved.
Forget Me will be officially released on September 9.
Capaldi played Forget Me after telling his fans: "I said at the start of the show it's been a while since I released new music, a very long time, three years in fact, but thankfully on 9 September that changes.
"Next week I release my first single from this next album. It's called Forget Me, so that's good news. As well as that, I am going to play that song for everybody here tonight.
"I am showing 20,000 people my song for the first time. I'm very nervous. No one has heard any of this music apart from you all here tonight."
In May, Capaldi was named on the ‘Young Music Rich List’ after amassing a £19 million fortune – just a couple of years after complaining that he was ‘skint’.
Capaldi placed at number 10 on the list, which was topped by former One Direction singer Harry Styles, who has amassed an incredible £100 million himself.
Last year, Capaldi placed at No.16 on Heat Magazine’s annual rich list – with a £17m fortune.
He released Divinely Uninspired To A Hellish Extent in May 2019, spending 10 weeks in the album top spot.
The record spawned a string of hits including Someone You Loved, Before You Go and Hold Me While You Wait, cementing him as one of the biggest newcomers in pop history.
It’s been a remarkable few years for the young Scot, who said in 2020 he was making good use of lockdown by writing new songs every day – because he “needs money”.