David Niven's book "The Moon is a Balloon" is a fun read. don't know how much is completely true.
I remember something about Joan Craword in the book, so I looked it up.
She was a big help to him when his wife died in an accident. She looked after his children in her home for weeks after their mother's death.
http://articles.sun-sentinel.com/1995-06-11/entertainment/9506060421_1_joan-crawford-mommie-mother-and-daughter