Jemima Khan has won Halloween, three weeks before the big day.

The activist and journalist attended the annual UNICEF Halloween Ball dressed as Melania Trump being groped by her husband, the Republican presidential nominee Donald Trump.

Jemima Khan attended the annual UNICEF UK Halloween Ball. Credit:Eamonn M. McCormack

"'Grab 'em by the pussy' #yourworstnightmare," she posted to Instagram ahead of the star-studded event in London.

Her uncanny appearance was offset by some severe smoky eyeshadow, a form-fitting white dress and a blow-up doll resembling Trump wrapping his arms around her.