The 20-year-old singer, who parted ways with Hemsworth in September this year, was in news at the time of the split for her raunchy performance at this year's MTV VMAs and her controversial 'Wrecking Ball' video, reported Contactmusic.
"As time has gone on and the anger subsided, Miley has really started to feel the pain of the split. She thought about writing some songs, but then decided why not write a letter to Liam to tell him exactly how she feels," a source said.
Cyrus and Hemsworth started dating in 2010 after meeting on the set of 'The Last Song'.
The couple were together for just two years before the actor popped the question in May 2012.