Jenkins, sent to the Cabinet Offices to pick up some Belgian papers, reflects:

The position of the King of the Belgians was delicate. Formally accepted as monarch of their country by the Belgian Government in exile, the royal portrait hanging in Kucherman’s office,  King Leopold, rightly or wrongly, was not, officially speaking, very well looked on by ourselves. His circumstances had been made no easier by a second marriage disapproved by many of his subjects. [MP 109/104 ]

King Leopold III of Belgium
from The Belgian Monarchy Official Website
© The Belgian Monarchy

Leopold III (1901-1983) was king of Belgium from 1934-1951. When Germany invaded Belgium in 1940, Leopold personally surrendered unconditionally on May 28, and chose to remain in Belgium rather than accompany the Belgium government into exile. Churchill publicly criticized his decision to surrender. Leopold said he felt compelled to stay in country with his subjects, but many Belgians, especially in the government-in-exile, saw him as a collaborator with, rather than as a prisoner of, the Germans

His first wife died in a car accident in 1935  In 1941 he married Mrs. Lilian Baels. The religious wedding ceremony did not comport with Belgian law, and their child was born 7 months later.

Both his actions during the war and his second marriage were unpopular with many Belgians, and he renounced the throne under pressure in 1951.