Moretti's maternal grandfather, Kevin Broadley, spent about a decade in Papua New Guinea in his twenties, working as a government lawyer before independence in 1975.
Broadley played rugby union there and did legal work for local people, Moretti told AAP.
"He (my grandad) was in tears when I told him I was selected," Moretti told AAP.
"He has got a lot of love for Papua New Guinea and when he was there it was quite rough."
The Parramatta prop had never visited PNG until earlier this week, but on Saturday he will debut for the Kumuls against Lebanon in Port Moresby.
Coach Jason Demetriou has named the 26-year-old to start in the front row.
Moretti played for Italy at the previous World Cup, qualifying through his father's ancestry, while his mother Julia and her sisters were born in PNG.
"It's not the most Papua New Guinean name, is it? You see the name Luca Moretti and you think he's Italian," Moretti said.
Demetriou has tracked Moretti for several years, and teammate Jack de Belin told him about PNG supporters' passionate following.
"He (de Belin) was another big reason why I wanted to go over. He's got some stories and said how it's a religion for the people," Moretti said.
Kumuls legend Adrian Lam was also one of Moretti's junior coaches.
Moretti and de Belin are the only PNG forwards to have played in the NRL this year. Lebanon will feature Eels teammate Jordan Samrani at centre.
"He's not got a target on his back, he's got a target on his head," Moretti said.