Forty-eight-year-old Andrew Bush was found dead on Saturday morning in his home in the southern Spanish town of Estepona.
Bush, who ran several jewellery businesses in Bristol, was shot twice in the head, the gun reportedly being found by police at the victim’s side.
All investigations are now centred on Bush's ex-lover, a blonde Slovakian model called Mayka Kukucova.
According to the millionaire's current girlfriend, Kukucova had opened the door to his home when they returned from a week away.
She called Spanish police when she was locked out by her boyfriend’s enraged ex and then watched her flee in one of Bush's luxury cars.
"We received a call at 2.10am on Saturday morning from the partner of the dead man because she could not gain access to the property," Estepona emergency services confirmed.
"Firefighters managed to get in and found the man lying dead inside with a gunshot wound to his head.
"Police are now probing the possibility she (Kukucova) may have let herself into the property while the occupant was away and waited for several days for him to return."
A neighbour, who asked not to be named, reportedly told the Mail Online: "All we know is that she's in her early twenties and comes from somewhere in Eastern Europe.
"From what I've heard the police are treating it as a terrible act of jealousy."