His Majesty is twice in serious trouble (6)
I believe the answer is:
crisis
'serious trouble' is the definition.
'crisis' can be an answer for 'trouble'. I'm not certain of the 'serious' bit.
'his majesty is twice' is the wordplay.
'his majesty' becomes 'cr' (I can't justify this - if you can you should give a lot more credence to this answer).
'twice' says to double the letters.
'is' duplicated is 'isis'.
'cr'+'isis'='CRISIS'
'in' is the link.
Can you help me to learn more?
(Other definitions for crisis that I've seen before include "Crucial point - decision time" , "Situation of extreme danger or difficulty" , "Crucial stage in a series of events" , "Dilemma" , "Time of intense difficulty or danger" .)