The gig, at London's O2 arena on Friday (21 December), saw Sinitta arrive on stage with men wearing T-shirts emblazoned with the phrase 'So Macho' – probably her best-known hit.
Wearing a white trouser suit, the 44-year-old 'Toy Boy' singer and I'm a Celebrity... Get Me Out of Here! star then proceeded to take her clothes off to reveal her underwear.
The '80s singer, who has dated Brad Pitt and Simon Cowell, is no stranger to appearing semi-naked.
At the Judges Houses stage of The X Factor in 2009, she appeared at Simon Cowell's house wearing only leaves.
Scores of bands reformed for the Hit Factory concert last night, which was in aid of Cancer Research UK. The evening also saw pop duo Kylie Minogue and Jason Donovan performing 'Especially For You' on stage together for the first time in 23 years.
Rick Astley, Steps and Bananarama also sang at the charity event.
Photo gallery - The Hit Factory Live Christmas Cracker:
Copyright: Ian West/PA Wire/Press Association Images