Alt-J have made the 'mystery' surrounding the Splendour In The Grass 'Mystery B∆nd' rather redundant.
Not only did everybody instantly guess that the cleverly disguised band were Alt-J as soon as the bill was announced (the ∆ is something of a giveaway, and Alt-J were already scheduled to be in the country for previously announced shows), but the band aren't even really trying to keep the secret anymore.
In a recent Reddit AMA, they responded with a :) when asked a question by a user posting as 'splendourmysteryband'. Today, they confirmed that you should never tell Alt-J your precious secrets by tweeting this:
Anyone know what the weather is going to be like at Splendour this weekend?
— Δ (alt-J) (@alt_J) July 22, 2013
So, in short, Splendour In The Grass organisers wanted to be this guy...
But ended up looking more like this guy...
Unless this is all a ruse, and they're just letting you think Alt-J is the mystery band until they reveal their hand, in which case they're actually this guy.