Director Roman Polanski has revisited the murder of his wife Sharon Tate by penning the introduction for a new book about her life.

Actress Tate was just 26 when she and her unborn child were killed by convicted mass murderer Charles Manson and his followers in August, 1969, a year after marrying Polanski.

Her sister Debra has now revived Tate's legacy by gathering friends, including her Valley of the Dolls co-star Patty Duke, Joan Collins and Jane Fonda to share their memories of the actress in Sharon Tate: Recollection, and Polanski was handed the honour of writing the foreword.

In the piece, obtained by the New York Post, he admits he still struggles to deal with the loss of Tate, writing, "Even after 40 years, it is difficult to write about Sharon.

"It is impossible, of course, to imagine what might have been if Sharon had lived. But this book allows me to remember what was."