In persistently
poor health, infirm, sick all of the time.
By
extension, looking sick or unhealthy.
It didn't matter if a prince or
princess was ugly or sickly or the village
idiot; as long as they were of royal blood, uncontaminated with that of commoners, that was all that mattered.
Carlos II of Spain is a case point for that problem; in delicate health,
retarded, impotent, and terribly ugly, Carlos was the end result of generations of inbreeding among the Spanish Habsburgs.
She was a sickly little girl; her nose was always running and she coughed a lot.