The 25-year-old actress - who played Emma Tregirls in the BBC period drama - said she had only found the courage to report the incident to the police last year after her “best friend” broke their pact to never see or speak to her attacker again.
Charteris has spoken out in an open letter to I Am Arla – a platform for “women who have experienced abuse, trauma and discrimination” to connect and share support.
The South African actress revealed her rapist was a “close friend, slightly older than me,” who she had known, “since I was 16 after meeting at a youth theatre group.”
She revealed the attack happened in 2015 after a night out to celebrate her best friend’s birthday party.
Charteris wrote: “Although I have struggled to say the word rape out loud for a long time, I knew that’s what had happened. Despite saying no numerous times, begging him to get off me, trying to physically pull him off, my flight mode was not attuned to protect me from a rapist that had the face of my best friend. So I just shut my eyes and passed out in terrified defeat. Only waking later to clean myself up and try and find my bottoms.”
The Mary Shelley star revealed she told her best friend the next morning and after deliberating, decided not to report the incident. But they agreed to cut the attacker out of their lives.
Charteris said she then discovered in 2018 that her best friend and her attacker were still in touch on social media. And when she confronted her friend, she told the actress she blamed her for having put her in an “incredibly difficult position for years”.
The Poldark star said the betrayal “broke me” and forced her to face what had happened to her and post-traumatic stress she had tried to bury for several years.
Charteris revealed she retired from acting and moved to New York in 2019 in an attempt to escape the ordeal.
But in December 2019, after seeking advice from lawyers and the charity Rape Crisis, she returned to London and reported the rape to the police.
Her best friend refused to give a witness statement and in March 2020 the police informed her they would not be pressing charges, adding: “It does not make him innocent.”
Charteris said: “When it comes to sexual assault and rape, I am not the worst case, I am not the first case, and sadly I will not be the last. But I am done letting the weakness of others define me.”
For confidential emotional support at times of distress, contact The Samaritans at any time by calling 116 123 or emailing email@example.com