"I'm sure it will be very bittersweet," the 33-year-old star told E! News at the Marie Claire Fresh Faces party on Tuesday night at Soho House in West Hollywood, Calif. "We all just want to honor Paul going back."
Production on the franchise's seventh film officially resumed in mid-March, less than four months after the death of Walker, who died in a fiery car crash in late November.
The late star had already shot a number of scenes for the film, his sixth appearance in the series (having not appeared in The Fast & the Furious: Tokyo Drift), when he was killed in a car crash Nov. 30 at the age of 40.
"I'm looking forward to being back with the Fast family, but there's definitely a key element missing," Brewster admitted with a heavy heart.
It's not known yet how the movie is going to handle saying goodbye to Walker's character Brian O'Conner, but he will be in the film, although Brewster could not divulge any details.
"That's all under lock and key. I'm not able to say anything," the mother of one admitted.
After Walker's death, Universal released a statement saying it is "our responsibility to shut down production on Fast & Furious 7 for a period of time so we can assess all options available to move forward with the franchise."
Vin Diesel has been keeping fans up to date with filming via his Facebook page and recently shared a video in which he's training with Walker's former jiu jitsu teacher for what he says will be the "best fight ever" in the Fast and Furious saga.
Fast & Furious 7 is due to hit theaters on April 10, 2015. (E! Online and Universal Pictures are both part of the NBCUniversal family.)