This is a sponsored post for T-Mobile
T-Mobile spent Tuesday filming the fourth episode of their Life is for Sharing campaign in London.
Famous for flashmobbing Liverpool Street, Heathrow and Trafalgar Square they've taken a different tack this time... but the concept and content of the video are being kept as secret as the design of Ms Middleton's wedding dress.
There are some clues over here. Can you guess?
The ad will be released on Friday at midday only online. And we'll be sharing it here.