Katherine's brother, actor Patrick Schwarzenegger confirmed the news in a video obtained by Entertainment Tonight on Sunday.
Despite the stress of giving birth during the pandemic, Schwarzenegger said she's been keeping her mind occupied by staying connected with fans and loved ones.
The baby on the way will be Katherine's first child while Pratt already has a son Jack, whom the actor shares with ex-wife Anna Faris.
Appearing on Ellen DeGeneres' show, Pratt said the film's script, penned by director Colin Trevorrow and Emily Carmichael, is "unbelievable" and he just can't wait to work on it.
Disney-Pixar’s Onward is all set to release the film in India on March 6.
This isn't the 'Game of Thrones' stars' first comment on the environment, he actor has been active in sharing concerns on the ongoing environmental crisis.