The 26-year-old Neighbors actor and 35-year-old Machete actress made headlines earlier this week when they were spotted kissing and cuddling on a yacht off the coast of Sardinia. A source tells E! News the pair were introduced by mutual friend Mohammed Al Turki two years ago, and have a history of hooking up.
"Michelle is super cool and laid back, and Zac has always been attracted to her because of that," the insider explains. "She's one of those people that everyone likes; she just gets on with all kinds of people and doesn't take the fame thing too seriously."
"Zac likes the fact that she is laid back and he can relate to her," the person adds. "He is attracted to her great attitude. They understand one another."
Efron and Rodriguez have been on vacation with entrepreneur Gianluca Vacchi in Italy. The actors were spotted on a romantic horseback ride Monday, and locked lips at a club later that evening.
Efron's new movie Neighbors debuted in theaters in May. The actor will next appear in John Grisham's The Associate, with Rodriguez to star in Fast & Furious 7 next year.
Notable deaths of 2014 [PHOTOS]