A Cape Town man has been arrested for allegedly cutting out the heart of his ex-girlfriend's current boyfriend before sitting down to eat it with a knife and fork.

Police in Gugulethu were alerted by victim Mbuyiselo Manona's neighbours who saw the suspect through the window sitting beside the man and "digging from the body and stuffing his face".

The unnamed suspect allegedly stabbed 62-year-old Manona in the chest and neck and bit him on the left side of the face, with police finding him with a piece of heart dripping from his mouth.

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The attack is believed to have been motivated by jealousy, as Manona had been dating the suspect's ex Nomonde Tshabalala, who has been left in a state of shock.

Western Cape police spokesman Captain Frederick van Wyk said of the incident, which took place at around 10.30pm on Tuesday: "On the scene they found a suspect, a Zimbabwean, eating the heart of a human with a knife and fork..

"[The police] were informed that the victim had been stabbed on the left side of his chest and in his neck, and had a bite mark on the right side of his face."

The neighbour who witnessed the attack told Times Live the man had been hired by Manona to install new windows at his house.

"When we got there the man kept muttering 'I am the king' and declaring his undying love for the woman," they said.

"He then cut the heart out and ate it before the police came and took him away."

Manona's sister, Thembela, said her brother had been in a relationship with Soloshe for more than four years and "didn't deserve to die in the hands of an animal."