I'm going to add my theory:
Norwegian buy into Monarch.
Monarch take-over the Norwegian short haul routes but branded as Norwegian i.e. the Monarch AOC remains intact and effectively becomes the Norwegian UK side of the business under the skin.
Monarch is the feeder to Norwegian long haul.
Norwegian immediately get the 737MAX fleet that Monarch has lined up, they get the crews they need, they get slots as Monarch itself is not sold off but effectively becomes an ACMI operator purely for Norwegian.
I'll get my coat....