Maxine McGill found flatmate Alice Ruggles on the bathroom floor of their Gateshead flat after she had been left to bleed to death by Lance Corporal Trimaan “Harry” Dhillon.
Dhillon, 26, cut Alice’s throat from ear to ear after he found out she had found happiness with another man and was jailed for life with a minimum term of 22 years at Newcastle Crown Court last month.
Speaking to the BBC, Ms McGill recalled the moment she made the gruesome discovery.
She said: “I just wanted somebody to try and help her, to bring her back but I knew deep down nothing was going to bring her back.
“It’s something that I don’t ever think I’ll be able to erase from my memory.
“What saddens me the most about it, is it shadows my memory of Alice when she was alive and when she was happy and that beautiful smile of hers.”
She added the scene that greeted her was “worse than what you see in films” and that she has not been the same since last October.
Dhillon, a signaller with the 2 Scots, drove 120 miles from Glencorse Barracks to confront Miss Ruggles and grabbed a long, sharp carving knife, cutting through to her spine.
Miss Ruggles, who worked for Sky in Newcastle and came from Leicestershire, tried to lock herself in the bathroom but Dhillon kicked it down.
Dhillon left the scene without dialling 999 but remembered to take her phone and the murder weapon, disposing of them on the way back to the Lothians.
He had claimed Alice had accidentally stabbed herself while lunging at him, but the jury took less than two hours to convict him of murder.
Jailing him, Judge Paul Sloan QC said: “You were pinning her down, probably by kneeling on her back, and in an act of utter barbarism you slashed her throat with a knife, slashed her at least six times, causing catastrophic injuries.
“Not a shred of remorse have you shown from first to last, indeed you were concentrating so hard on getting your story right when giving evidence, you forgot even to shed a crocodile tear.”
A trust has been set up in Alice’s name with the aim of raising money for good causes and to provide training and education about issues such as stalking.