Adele surprised fans when she made a rare public appearance on Wednesday night.
The Skyfall singer, 26, was attending Katy Perry's gig at the 02 Arena in London and was clearly a special guest of honour.
Katy took to Instagram to post a photo of the pair after her performance, captioning the backstage snap, "...And on the 2nd LDN show the Queen graced me with her presence."
Adele, who is proud mum to 19-month-old son Angelo, in turn praised Katy for her concert, although she seemed just as excited by an encounter with an inflatable children's character from In The Night Garden.
"Katy Perry was supreme tonight! But UK mamas look who I saw tonight!" wrote Adele next to the image of herself striking a pose at the venue.
Other celebrities who have attended Katy's four-night residence included Robert Pattinson, Sam Smith, Nick Grimshaw and Jessie Ware.
Katy Perry was supreme tonight! But UK mamas look who I saw tonight! pic.twitter.com/iccKIi88et— Adele (@OfficialAdele) May 28, 2014