meaning of "the thought was almost revolting''

"The Portrait of a Lady", by Khuswant Singh is about the manner in which children perceive adults. Singh's had always seen his Grandmother to be white-haired venerable lady. According to the Singh, his Grandmother was a deep and "spiritual lady".  Nevertheless, the fact that she was actually beautiful in her youth, was a notion that Singh could not conceptualize. Children do not like changes and find it difficult to accept things that they cannot visualize. When Khuswant Singh was a child it was easier for him to perceive his Grandmother as an old woman than a young and beautiful lady. To a child this thought would naturally be "revolting". This story reflects on the relationship of Singh with his Grandmother and overall, on the emotional of relation shared between grandparents and their grandchildren.