The 23-year-old British royal went to the bash at exclusive London nightspot Barts, in Chelsea, dressed as an elf and after she and her four friends drank some glasses of wine and cider, she proceeded to jump onto the bar and start dancing.
A source told The Sun newspaper: "It was quite a sight. The DJ was playing the Bon Jovi song 'Livin' On A Prayer' and Beatrice started conducting the punters with her hands. She was really getting into it and everyone was singing along."
Although Beatrice - whose parents are Prince Andrew and his ex-wife Sarah Ferguson - came dressed as an elf she eventually ditched her costume and changed into regular clothes to enjoy the rest of the night and according to one fellow reveller she had a "brilliant time".
Barts bar is a popular hangout with friends of the Royal Family and is owned by Charles Gilkes, who is an acquaintance of Prince William's wife Duchess Catherine.