The 'X Factor' boss is holidaying on a £30 million yacht off the coast of St Barts with a group of people including former love Sinitta, his close friend, gaming mogul Andrew Silverman and his wife Lauren and Zeta, who has been referred to as his "date".
A source told the Daily Mirror: "Simon has known Zeta for a few years and the pair have always remained in touch.
"She is with him for the New Year break and has been keeping him company. Zeta fits in really well with his gang and she makes him laugh. They have a real giggle together."
Zeta, 43 - who starred in 'The Fifth Element' - has a 19-year-old son Laurence with former husband Francois, a diamond heir.
Simon's fiancee Mezghan Hussainy - who hasn't been seen with the 52-year-old mogul for over two months - is not on the trip.
Last year, Simon claimed he was "not sure" whether he is still engaged to the 38-year-old beauty, and his 86-year-old mum Julie also revealed she has not seen Mezghan "for months".
When asked about the couple's relationship, she said: "I honestly don't know, I've hardly seen him. I saw him three days last week and he was working constantly, of course, every day in the studio while he was here. I met him briefly for dinner and he didn't discuss anything with me. He's very private, Simon, about his personal life. He won't talk about it, so I'm as much in the dark as everyone else.
"I haven't seen Mezhgan for months - she's been in America all this time and I don't know if she's working or what, because she has her make-up company and is very busy."