Louisa Johnson absolutely SLAYED on the red carpet at London's Monster Mash-Up This image appears in the gallery:#MonsterMashUp 2016: ALL The Photos From Last Halloween's BIGGEST Party 35. Louisa Johnson absolutely SLAYED on the red carpet at London's Monster Mash-Up (Pic: PA) 77 images See the full gallery: #MonsterMashUp 2016: ALL The Photos From Last Halloween's BIGGEST Party