The Good Charlotte rocker, who was joined by his twin brother Joel Madden, opened up for the first time since being spotted with the Sex Tape actress.
"You guys are both maturing now, you've got families, you're both in love," Nova FM hosts Fitzy and Wippa said to the 35-year-old brothers, adding, "You both got girls. Both got chicks and stuff."
Nicole Richie's husband then said, "Life is good, man," while Benji added, "We're lucky guys!"
Benji and Diaz were first photographed together on June 3, when they stepped out holding hands while grabbing coffee in New York City.
"Nicole thought they'd click," a source tells Us Weekly of how the couple met.
In an interview with Ryan Seacrest on KIIS FM's On Air With Ryan Seacrest last month, the rocker stayed more mum about his relationship with the leggy blonde.
"Well, Ryan, there's only one way to find out," Benji told Seacrest when asked about his romance with Diaz, jokingly adding, "You've got to play Ryan's Roses…that's still a radio phenomenon."
Diaz has previously dated Alex Rodriguez, Justin Timberlake and Jared Leto.