"She's absolutely devastated," a source tells us.
The private celebrity pairing first sparked romance rumors around last year's holiday season when they were spotted out and about in the actor's hometown of Tulsa, Okla. Rachel and Bill would confirm those rumors by stepping out together at the 2020 Golden Globes in January, and by all accounts the couple was still very much in the honeymoon stage a month later.
"They spent Valentine's Day weekend in Orange County, Calif," an insider shared with E! News at the time. "It was a quick getaway, but time for the two of them to be together without any distractions. Rachel is very happy dating Bill and is excited about being with him."
"He treats her very well," the source added.
Rachel, 38, and Bill, 42, first crossed paths when they co-starred in the 2013 flick The To Do List. At the time, however, both were in relationships.
In 2017, The O.C. actress and Hayden Christensen split after 10 years together. They continue to co-parent their 5-year-old daughter Briar Rose. Prior to dating the Barry star, Rachel was linked romantically link to The Bachelor's Nick Viall.
Hader filed for divorce from Maggie Carey in 2018 after 11 years of marriage. They share three daughters—Hannah, 10, Harper, 7, and Hayley, 5.
On the topic of dating in the public eye (and as a single mom), Bilson said in a 2019 interview on Viall's podcast, "[Briar] has not met anyone as of yet and it would have to be someone I know I'm going to be with. It would have to be a very serious relationship."
"She's my world and I talk about her all the time," the actress explained at the time. "How f--ked up would it be if I hid that? If you're going to pursue something with someone, they have to be interested in the kid or be willing to be around the kid."
E! News has reached out to reps for both Rachel and Bill for comment.
People was first to report the news.