Lisa O’Brien was working for Christopher Newman, whom she knew as “the Professor”, at his Dublin clinic at the time.
She told the jury at Inner London Crown Court how he would scan through Georgina Eager’s mobile phone and become angry if men called asking for a massage from her.
The 62-year-old is accused of repeatedly stabbing Georgina and leaving her dead in her locked bedroom in May 2003.
The Indian-born British citizen, also known as Saph Dean, denies murder, claiming self-defence.
Georgina, 28, from Trudderbridge, Co Wicklow, worked for Newman and lived next door to his clinic in St Peter’s Road.
Soon after she joined his practice in summer 2002, the pair became lovers.
Ms O’Brien knew Georgina when she was working for Newman for a couple of weeks before the alleged murder.
She told the court: “She was a very pleasant girl, very easy-going. She really admired Professor Dean. She spoke very highly of him.
“She told me that coming to work for him was a great thing because I’d be learning so much. She said he was just a great person and a wonderful teacher.”
Asked about her impression of the defendant, she answered: “He could be a bit domineering I would say, a bit arrogant.
“If you did something wrong he would correct you and he’d be very quick to tell you, ‘That’s not the way to do things’. He was quite snappy.”
Ms O’Brien said neither told her about their affair, but added: “It didn’t seem like the normal employer-employee relationship.”
She added: “He would look through her phone. I remember one occasion when they were having an argument about who she was ringing.”
On another occasion Ms O’Brien was discussing Newman’s personal history.
“He said women usually ran away from him.
“I laughed, like it was a joke. But he seemed very serious. I just felt very uncomfortable.”
Under cross-examination by defence lawyer Andrew Smiler, she said that her boss had banned massages from the clinic, saying that men who came for them “want different things”.
The court also heard from Gary McSweeney, who spoke to the defendant just a few hours after the alleged murder on May 22, 2003, and described how he had been agitated at the time.
Mr McSweeney, a physiotherapy trainer, had travelled from Limerick to buy one of the portable physio beds that Newman sold.
He told the court he had rung Newman’s mobile phone around 11am - on the same day that the therapist was said to have murdered Georgina in the early hours of the morning.
He said: “He got very agitated and said, ‘No, no, no, no, no business today. Do not come out today’.”
Newman, formerly of St Peter’s Road, Dublin, now of Catford, south-east London, sat with his head bowed throughout yesterday’s evidence on the third day of his trial.