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.
Since welcoming her son with partner Simon Konecki, Adele has shied away from the spotlight. The doting mum has made just a few appearances at global events including the Academy Awards and the Golden Globes.
Last December, Adele, who is worth £45million, made a rare public appearance to receive an MBE for her services to the music industry. She was presented the Most Excellent Order of the British Empire award by Prince Charles.
The Someone Like You singer looks set to step back into the limelight as she gears up to release her third album later this year.
Earlier this month Adele posted a cryptic message, tweeting, "Bye bye 25... See you again later in the year x". The star's two studio album titles to date have been named after her age at the time they were written.