Kumar married four times. His first wife was Bengali singer and actress Ruma Guha Thakurta aka Ruma Ghosh. Their marriage lasted from 1950 to 1958. His second wife was actress Madhubala, who had worked with him in many films including his home production "Chalti Ka Naam Gaadi" (1958) and "Jhumroo" (1961). When Kumar proposed to her, Madhubala was ill and was planning to go to London for treatment. She had a ventricular septal defect (hole in the heart), and he was still married to Ruma. After his divorce, the couple had a civil wedding in 1960 and Kumar converted to Islam and reportedly changed his name to Karim Abdul. His parents refused to attend the ceremony. The couple also had a Hindu ceremony to please Kumar's parents, but Madhubala was never truly accepted as his wife. Within a month of their wedding, she moved back to her bungalow in Bandra because of tension in the Kumar household. They remained married, but under great strain for the remainder of Madhubala's life. Their marriage ended with Madhubala's death on 23 February 1969.