The movie that Karan and Nisha watch at the cinema, when Timsy is spying on them is "40 Carats (1973)".
Shashi Kapoor, who played Shashi Sehgal in this movie, is in real life the youngest paternal uncle of Rishi Kapoor, who played Karan Saxena (Kannu). That was the actual reason of their greatly identical looks.
Raakhee who is five years older than Rishi plays his romantic lead in the movie. Interestingly Rishi who was always paired with younger heroines has played the romantic lead to all the top heroines of the 70s in one movie each, though they were considered to be too mature to be paired with him on a regular basis. Raakhee in Doosra Aadmi and Zeenat in Hum Kisise kum nahin, both in 1977 and later in the 80s with Shabana Azmi in Rahi Badal Gaye, Hema malini in Ek chadar maili se, and Rekha in Azaad Desh ke ghulam. He was never paired opposite Smita Patil though.
The film was remade as Dil Ne Phir Yaad Kiya in 2001.
There were several stories that Rakhee was involved with Ramesh Talwar during the making of the film.