When they returned to India, amok 'Vedic marriage' was instituted for public consumption. On this subject, writes M.O. Mathai (a longtime Private Secretary of Nehru) in his renowned (but now suppressed by the GOI!) Reminiscences of the Nehru Age' on page94, second paragraph: "For some inexplicable reason, Nehru allowed the marriage to be performed according to Vedic rites in 1942. An inter-religious and inter-caste marriage under Vedic rites at that time was not valid in law. To be legal, it had to be a civil marriage."
It's a known fact that after Rajiv's birth Indira and Feroze lived separately, but they were not divorced. Feroze used to harass Nehru frequently for money and also interfere in Nehru's political activities. Nehru got fed up and left instructions not to allow him into the Prime Minister's residence Trimurthi Bhavan. Mathai writes that the death of Feroze came as a relief to Nehru and Indira.
The death of Feroze in 1960 before he could consolidate his own political forces, is itself a mystery. Firoze had even planned to remarry.
