The 47-year-old "Spinning Around" hitmaker was joined by Joshua Sasse, 28, as she sang her version of "Only You" for excited guests at the Warner/Parlophone party at the Ring O' Bells pub, Somerset, south west England, reported Femalefirst.
The party - which also featured performances from Duran Duran - was held in the pub as Parlophone Records owner Miles Leonard has a part-share in the venue.
Unsuspecting members of the public were even invited to the party.