The couple were together in bed the night after the 25-year-old policewoman was allegedly attacked by a colleague following a "toffs and tarts" party at a police section house on New Year's Eve, 1993.
"There were marks on her left wrist and bicep - but the thing that grabbed my attention was a mass of bruising on her left breast. It was black with yellow round the fringes," the officer told an Old Bailey jury.
"There were four fingermarks on the side of the breast. I have seen a lot of bruising from the job I do but I was shocked at the intensity.
"I was furious. I was so angry that someone should have done that. She said someone had tried to force themselves on her but she managed to fight them off. I wanted to know who had done it. She said initially she did not know. I was quite frantic to find out what happened," the officer told the court.
Three months after the party, his girlfriend made a formal complaint which resulted in a fellow officer - Michael Seear - being accused of raping her. PC Seear, 25, of Lightwater, Surrey, denies the charge.
The woman's boyfriend told the court that on the night after the party his girlfriend had undressed with the lights off.
"She had no inhibitions about nakedness - I thought I had done something wrong or irritated her. I asked her `Why are you undressing with the lights out - are you afraid to be seen naked or don't you want me to see you naked?'
"She was very quiet and said she had something to tell me."
She made him promise not to pursue the matter. Then she got into bed, undid the top of her pyjamas and showed him the bruises.
The boyfriend told the court he was "peppering" her with questions to find out what had happened, but her answers had been evasive. She told him: "If you knew who it was, you would know why I can't tell you."
The officer said the woman had not wanted him to know what had happened. "There were other concerns - for her own position as a newcomer to the section house and as a probationer police officer. She did not want to make waves.
"She was agitated and shocked, but I got the impression she wanted to carry on as normally as she could."
The trial continues today.Reuse content