Adele refused to use the London Underground for almost 20 years.
The 35-year-old pop superstar — who was born and raised in the UK capital — stopped using the Tube in 2005 after the city's public transport network was hit by a series of suicide bombings which targeted underground trains and a bus and killed more than 50 people.
The singer explained her fears while she was onstage for her Weekends With Adele residency in Las Vegas. She said: "I haven't really been on the Tube in England, not since I've been famous. It is since we had a terror attack there. I have been scared because I get claustrophobic."
However, Adele was forced to confront her fear of the Underground last year when she was back in the UK as she needed to travel from central London to the O2 Arena in North Greenwich and did not have time to take a taxi.
She added: "[During] the last break [from the residency shows], I went home to London and I wanted to go to the Mamma Mia party. It's at the O2.
"So it was Friday night and I had an appointment before. So I had to get there in like 45 minutes and it's like a two hour drive really in traffic.
"So I had to get on the Tube, my appointment required me to be in full hair and make-up. So I very much looked like Adele the singer.
"I got on the Tube and I had a mask on. I did have lots of security guards with me in fairness and a few friends, but we were all very under the radar and I felt right at home. You'll never guess what happened, but I ... fell asleep!"
Adele added that it was actually a very positive experience for her. She went on: "Anyways I loved it. And then I got to the O2 and I had to walk through thousands and thousands of people. People started recognising me then, but I was ... out of time."
She added: "I wasn't even scared to be on the Tube. I loved it. It reminded me of my teenage years."