Well we had an attempt at putting them back together. Sir George was giving out friendly signals but Master Boris was showing lots of fear aggression and lunging.
It seems like Master Boris had a fright when Sir George put him back in place. Sir George however is acting like "what's the problem?" I stopped the bonding session, probably prematurely, because I couldn't bear to see my little boy looking so afraid.
They are ok as neighbours except for the initial confusion about where the rest of the cage had gone. Both had crashed into the dividers and Sir George was seen posting some extra yummy bits of hay with seed heads on over to Master Boris's side

I suppose I'm hoping that Master Boris will calm down and realise that Sir George is not out to get him.