Despite guests being asked to RSVP by the start of last week, Harry and Meghan have kept quiet on their intentions.
Jobson writes in his book that King is upset by the continued divisions between the Sussexes and the rest of the Royal Family but is becoming increasingly pessimistic about the chances of reconciliation.
“The fact is that Charles is deeply saddened by the widening gulf between him and his youngest son,” he wrote.
“Without doubt, Harry’s stream of complaints have threatened to upset the harmony of the new reign. Each TV interview to promote his autobiography has made the chances of healing the rift with his father seem less likely.”