"They're my best friends," America Ferrera tells PEOPLE in the latest issue of her Sisterhood of the Traveling Pants costars Blake Lively, Amber Tablyn and Alexis Bledel.
In fact, the stars have been friends for so long that Ferrera often forgets they came into each other's lives because of the 2005 film and 2008 sequel.
"When I'm out with my Sisterhood girls, I think, 'Why are people staring?' Then it hits me, 'Oh! It's because we are the Sisterhood girls,' " says the actress, who has revealed that a third Sisterhood movie is in the works.
"Mark [Indelicato], who played my nephew on Ugly Betty, is often my date when I'm in New York," Ferrera says of her former ABC dramedy costar. "When people look at us strange, I have to remember that they are seeing Betty and Justin."
For more from Ferrera – including how she likes to spend date nights with husband Ryan Williams – pick up the latest issue of PEOPLE, on newsstands Friday
"My cast mates and I get together and live-tweet at someone's house or apartment," she says of how the cast of the hit NBC comedy spend their Monday nights. "We already finished filming the first season so it's nice to stay connected that way."
Superstore airs Mondays (8 p.m. ET) on NBC.