According to the Daily Mail, the 41-year-old actress feels betrayed by the couple's reported relationship, which was first reported by OK! Magazine.
"It started as a convenient rebound but blossomed into something very real and exciting. Chris and Olivia have a genuine connection…She and Chris really like each other. They both want to see where this goes," a source close to the couple said.
On her podcast Anna Faris is Unqualified, Faris had revealed in 2016 that Munn was her husband's "dream woman" due to their common interest in eagles.
In November, Faris and Pratt filed for divorce after eight years of marriage, citing irreconcilable differences. The documents listed July 13, 2017 as their separation date, meaning that the couple had been apart for nearly a month before they announced their separation in August.
"Anna and I are sad to announce we are legally separating. We tried hard for a long time, and we're really disappointed," Pratt wrote in a joint statement. "Our son has two parents who love him very much and for his sake we want to keep this situation as private as possible moving forward. We still have love for each other, will always cherish our time together and continue to have the deepest respect for one another."
The couple met in 2007 on the set of Take Me Home Tonight, a film where they played one another's love interests. In 2008, they became engaged, tying the knot the following year in Bali. Their son, Jack Pratt, was welcomed in 2012.
Faris and Pratt have filed legal documents asking for joint custody of their son.