Anastacia was spotted singing with fans on Sunday night as she walked the streets of London’s Soho.
The 53-year-old star belted out her hit Left Outside Alone after revealing she “accidentally” stumbled into a “really fun bar”.
Once inside, she posed for photos with fans who then got into a singalong with her later on in the night.
When one didn’t believe it was her, the star – wearing a denim jacket and her signature orange tinted sunglasses - launched into song.
“Do you believe it’s me now?” she asked the crowd, before they all joined in singing her 2004 hit.
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Sharing the video on TikTok, one fan wrote: “When you bump into @freakanastacia outside your local and she gives you a private concert in the street.”
The clip has since been viewed more than 1 million times and Anastacia shared it on her own social media pages.
Explaining how it all came about, she took to Instagram to tell her 237,000 followers: “Hey everybody, I want to tell you a funny story.
“I was needing some coffee and doing all the work for the tour. And all of a sudden I saw this really fun bar, so I accidentally went in – and I found so amazing people. It was really cool.”
“I’m going to share some of it with you now. I love my fans!” she said before blowing a kiss to the camera.
Anastacia’s I’m Outta Lockdown tour starts in Lisbon on September 15 and ends with a gig in the Faroe Islands on November 19.
The UK leg of the tour kicks off in Brighton on October 31 before heading to Birmingham, Ipswich, Manchester and Cardiff.
She is back in London to play at the Hammersmith Apollo on November 8 followed by more gigs in Bath, Oxford, Stoke-on-Trent, Newcastle and Glasgow.
She has said she is “so excited” to get back on stage after struggling with a lack of work during lockdown.
The US star was famous all over the world back in 2000 when she released her hit single I’m Outta Love.
But she has suffered with several health problems in recent years, which led to her stepping out the spotlight.
In 2002, her career would come to a sudden halt when she was diagnosed with breast cancer.
The star took two years off for gruelling radiotherapy, and when she recovered returned with a pop-rock album led by single Left Outside Alone, which was a major success.
But sadly her illness caused her voice to lose its power and she became unable to record music, instead focusing on writing lyrics instead.
She went on to headline four tours and win an MTV Europe Music Award.
Aged 39, bad luck would strike Anastacia again as she was diagnosed with the heart condition superventricular tachycardia, which causes the heart to beat faster than normal.
Then in 2013, the worst happened - her breast cancer returned and she underwent a double mastectomy.
Incredibly, she now has the all-clear from cancer after a long battle comprising ten procedures and five surgeries and announced her comeback tour for 2022/23.
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