Celine, 51, wowed thousands with her set at the festival in London on Friday night (05.07.19) and after she left the stage concert goer Adele didn't want the fun to stop.
The 'Hello' hitmaker ended up in one of the festival promoter's offices with her friend Alan Carr and his husband Paul Drayton and Adele was heard belting out 'My Heart Will Go On' which Celine recorded as the theme song to 1997 blockbuster movie 'Titanic'.
A source told The Diary column in the Daily Mirror newspaper: ''Adele hotfooted it backstage with her mates, including best mate Alan Carr's husband Paul Drayton.
''They all set up shop in one of the festival promoter's offices to carry on the party ... which they duly did. The night was already in full swing when the singing started ... which went on and on and on.''
Adele has been a long-time fan of Celine and went to see one of her Las Vegas residency shows in January 2018 and got to meet her backstage.
Posting about the meeting on her Instagram account afterwards, Adele wrote: ''Queen Celine! What a show, an absolute highlight of my life, thank you so much for the attention to your crowd and insane humor. Happy new year lady x''
Ahead of their upcoming tour, and prior to the release of their long awaited album, Smoke Fairies played a great warm-up gig at Elsewhere in Margate.