Pop star plays 'kooky aunt' persona.

If you were setting out to deliberately make an advertisement "go viral", the chances are that you might opt for a whole load of cute kitties and perhaps throw in somebody really famous.

Well, the advertising team behind the newest promo for Diet Coke are way ahead of you - because they've just unleashed a promo which features pop star Taylor Swift in a room full of cats.

T-Swift announced it to the world on Twitter, writing: "Behold, the Diet Coke ad that depicts my perfect world. Featuring a new song and Olivia, who is now a cat actress."

The promo begins with Swift sipping a bottle of the beverage as she dangles a piece of wool in front of her beloved moggy Olivia Benson.

But each time she takes a swig and closes her eyes, the number of cats has multiplied when she opens them again - until all we can see is her arm emerging from a sea of furry felines clutching the empty bottle.

It closes with a plug for her new album 1989 - and the ad's soundtrack suggests there will be at least one upbeat pop number on the collection.