Father-Daughter On Screen, Crush Off-Screen
Despite playing father and daughter in the movie, Christopher Plummer, who played Captain von Trapp, and Charmian Carr, who played Liesl, allegedly had a love affair off-set despite the 13-year age gap between them. And Plummer was married at the time. Unsurprisingly, this revelation attracted a lot of attention from both the media and fans of the movie, but the two were never seen being affectionate in public.
Source: Twentieth Century Fox
However, in an episode of the Oprah Winfrey Show years later, Carr joined Julie Andrews and the seven actors that played the children and revealed the feelings she’d had as a 21-year-old girl. “I had a huge crush on him,” she said. “He was so perfect, and he spoke with this perfect British accent.” She denied the relationship ever became physical, though.