Thaxter, who played Clark Kent's mum in the 1978 Superman movie, died earlier this month (Aug12) and now her daughter, Skye Aubrey, has opened up about her mother's fling with Clift, who many Hollywood historians believe was gay - even though he never officially came out.
Actress Aubrey tells The Hollywood Reporter her mum shared a New York apartment with Clift when both stars were 20, and had dreams of becoming his wife.
She tells the publication, "He told her he didn't really think he could ever be married."
Clift stayed true to his word and never married, while Thaxter wed twice.
The star, famed for her role in 1978 blockbuster Superman, passed away on Tuesday (14Aug12) in Longwood, Florida, nine years after she was first diagnosed with the condition, according to website Variety.com.
Thaxter began her career on Broadway as a teenager in the 1930s before turning to movies with roles in 1945's Bewitched and Thirty Seconds Over Tokyo in 1944.
She later appeared in TV shows such as Alfred Hitchcock Presents, The Twilight Zone, and The Fugitive. Her most famous role was playing Clark Kent's adoptive mother, Martha, in 1978's Superman opposite Christopher Reeve as the Man of Steel.
Thaxter, who has a star on the Hollywood Walk of Fame, was last seen onscreen in a 1992 episode of popular TV show Murder, She Wrote.