Page 95 from the book:
And in the end he let her die (his wife) rather than allow British doctors to give her a shot of penicillin (while his inner voice told him that it would be all right for him to take quinine). He disowned his eldest son, Harilal, for wishing to marry. He banished his second son for giving his struggling older brother a small sum of money. Harilal grew quite wild with rage against his father, attacked him in print, converted to Islam, took to women, drink and died an alcoholic in 1948. The Mahatma attacked him right back in his pious way, proclaiming modestly in an open letter in Young India, Men may be good, not necessarily their children."
I hope his grandson knows he's alive because his father rebelled against Gandhi.
You raise an interesting point: if his father converted to Islam, is Arun Gandhi a Muslim, or Hindu?