Not surprised about HAIM, she asked us (via Twitter) about them a few months ago, remember? I think they have some affiliation with Roc Nation because they're also playing that Charity gig with Beyonce at Wembley stadium later on this Summer.
A more popular/current opening would've been cool, but if Hiam does have some sort of affiliation with RN then I'm not surprised they're the ones opening. Her European leg is pretty much sold out, so its not like they need the help to sell tickets so this is another opportunity for RN to promote a new artist. Just like they did with J. Cole during the US leg of the LOUD Tour and Alexis Jordan for the Australian leg of the LGOE Tour.
