The 23-year-old looked like she wanted to experience being a Londoner so decided to ditch her car and travelled on the underground.
The Man Down hitmaker appeared to be in good spirits as she chatted to fans, posed for pictures and talked about her gig at the O2 Arena in Greenwich.
A source told British newspaper The Sun: 'Fans couldn't believe they were sharing a carriage with a world famous pop star.
'She was just like any other passenger, except accompanied by a huge entourage. She was happy to pose for snaps and talk about the gig. She was so down to earth.'