Can you add a 2012 Hyper-V 2 node cluster to an existing 2008 R2 Hyper-V Cluster

We have a 4 node Windows 2008 R2 HA cluster.  We have 2 new nodes that we'd like to install Windows 2012 Hyper-V on before we upgrade our current cluster to 2012.  Can we do this?  Or do we need to upgrade our 2008 R2 nodes to 2012 first, then add the two new nodes.

Thanks

Ben