Jess Glynne partied with the Spice Girls until 7am on Sunday before pulling out of the Isle of Wight Festival that night saying she was suffering “exhaustion”, we can reveal.

Festival boss John Giddings has criticised the singer’s “shocking behaviour”, and declared: “She will never be booked to play the Isle of Wight again.”

Jess, 29, who supported the Spice Girls at Wembley Stadium on Saturday, stayed for the star-studded backstage party, which included singer Adele, 31.

Jess was seen leaving Wembley at 5am on Sunday with a group of friends and Spice Girl Mel B.

They continued the party at a nearby hotel until at least 7am.

(Image: WireImage)

A car came to pick up Jess at 9am to take her to the Isle of Wight. She was due on at 6.30pm, and her band were there and the stage was prepared for her set.

At 6.40pm, Mr Giddings went on stage to announce her set was off, leaving some fans in tears.

Mr Giddings told the Mirror: “It shows no regards for people that bought a ticket. It’s so sad that an artist would do that to their fans.

“She’s let them down.”

Her management initially blamed her no show on exhaustion.

Jess, who has sold more than 13 million records, and was nominated for Best British Single for I’ll Be There at this year’s Brits, put her decision to cancel down to anxiety.

(Image: Redferns)

She said: “I got ready and was about to head to stage, but I just couldn’t do it.

“I was incredibly weak and full of anxiety. I can’t help that my body sometimes gives up on me. I am so, so gutted, sorry and upset I couldn’t perform.”

An insider said: “Jess was sitting in the dressing room and it was quite apparent that she was incapable of getting on stage.

It wasn’t because she was ‘exhausted’.”

(Image: Twitter)

Other stars at the Wembley backstage party after the Spice Girls’ final show included Downton actress Lily James, 30, DJ Chris Evans, 53, and singers Will Young , 40, and Niall Horan, 25.

Jess had pulled out of the Isle of Wight festival in 2015 when she had vocal surgery.

Last month she failed to show at BBC Radio 1’s Big Weekend in Middlesbrough after losing her voice.

Mel B’s representative last night declined to comment.