He is accused of murdering his 39-year-old American marketing executive girlfriend Gabriela Kabrins Alban, at a boutique hotel in Camps Bay where they were staying, on July 29, 2015.
Hotel staff at the five star Camps Bay Retreat hotel found her body in the afternoon.
Novella was not in the room, but was arrested later that day.
Alban had been strangled and had suffered blunt force trauma to her face and defensive wounds on her arms.
In his plea statement, read out to the court by defence lawyer William Booth, Novella denied that he intended killing Alban, and claimed "diminished responsibility" due to drug intoxication.
"At the time of the said incident I was in an abnormal mental state as a result of the intake of substances. These substances had a disinhibiting effect on me, causing me to respond in an abnormal manner".
Alban was referred to Valkenberg Psychiatric Hospital after his arrest and was placed under observation.
A "unanimous decision" by a panel concluded diminished responsibility. His statement revealed details of his relationship with Alban, whom he had been romantically involved with since 2013.
He said she had lived with him in Guatemala for about a year in 2014 and they travelled together often.
In April 2015, Novella arrived in South Africa on his own and later went to a "cleansing clinic" in Magaliesberg.
While at the retreat, he made arrangements for Alban to attend the retreat with him so that she could receive treatment for her Lyme disease.
On the 10th of July, 2015, she arrived in South Africa and checked into the Camps Bay hotel.
Novella joined her the next day. The two subsequently travelled to Rome, but returned to Cape Town on July 25 and returned to the Camps Bay Retreat Hotel.
Novella claimed they were in love with each other and that her death devastated him.
"I have up until now, spent many hours of agony and trauma thinking about her," he said.
In his admissions to the court, he confirmed that Alban's cause of death recorded in the post-mortem report was not disputed.
It stated that her body had "signs of blunt force trauma as indicated by multiple bruises on the body specifically distributed on the neck, the upper and lower limbs".
The post mortem report indicated that there were signs of blunt force trauma to the neck and evidence of manual strangulation.
There was also "injury in the genital area in keeping with recent sexual penetration".
Alban's family flew in from America to witness court proceedings.
Her mother and stepfather, Doris Weitz and Alexander Williams, as well as her father and stepmother, Howdy and Linda Kabrins, said they were determined to see justice done.
Alban's father, Howdy Kabrins, is expected to be the first witness to take the stand.
Novella avoided eye contact with Alban's family members. Dressed in a well cut suit and tie, he instructed his lawyer that he no longer needed a Spanish interpreter.
During his bail application, his request for an interpreter caused several delays.
Novella is from a wealthy and prominent Guatemalan family who have run a successful cement business for over a hundred years.
He was denied bail in May last year as he was deemed a flight risk, with access to funds that could allow him to evade his trial.