The claim was made by a source close to Chambers as reported in a new Vanity Fair expose, which details a series of allegations Hammer has faced in recent months.
The article states: “According to a friend close to Elizabeth, Armie confessed to being unfaithful shortly after his son’s birth—but claimed it was a one-time offense.
“Years later, this friend says, Elizabeth found evidence of an affair Armie was having with a costar.”
The couple have two children together, a daughter born in 2014 and a son in 2017.
Hammer has starred in several films, including Home Shopper, Sorry to Bother You, Hotel Mumbai, On the Basis of Sex, Wounds, Query, Rebecca, We Are Who We Are and Crisis.
It is not known which costar or which film the source was referring to.
Hammer and Chambers announced their split with matching statements shared on their respective Instagram profiles.
“Thirteen years as best friends, soulmates, partners and then parents,” the statement read.
“It has been an incredible journey, but together, we’ve decided to turn the page and move on from our marriage. As we enter into this next chapter, our children and relationship as co-parents and dear friends will remain our priority.”
They continued: “We understand this news lends itself to public dialogue, but in the interest of our children and our family, we’re asking for privacy, compassion and love during this time.”
Hammer has not responded to the allegations made in the Vanity Fair article, which features a quote from his ex-girlfriend, Paige Lorenzo, who told the publication she felt “really unsafe” with him.
The Independent has contacted a representative for Armie Hammer for comment.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies