Britney Spears tweets behind-the-scenes photo from Glee set

Britney Spears has given her Twitter followers a sneak preview of her upcoming guest-appearance on the Glee episode devoted to her hits – by posting an on-set photo of herself on the social networking site.

The pop princess tweeted the snap of herself wearing glasses and sporting long hair extensions on the McKinley High set with her assistant Brett.

Spears tweeted: “What's up GLEEKS? Having so much fun on set! Can't wait for you guys to see the episode!”

Show co-creator Ryan Murphy has confirmed that the episode will be based around the Glee cast going to the dentist where, after being anaesthetised, they have “fantasies” and hallucinate about Spears.

Murphy has promised the episode will be “so reverential” about the Toxic singer and will not refer to the troubles she has faced in her private life.

He said: “It’s about her music and it’s not about her personal life.”