Reps for Hader did not immediately respond to Fox News' request for comment. A rep for Bilson could not be reached.
In January, the couple made their relationship red carpet official, stepping out at the Golden Globe Awards together after previously sparking romance rumors just before Christmas.
The two Hollywood stars had the Internet buzzing after they were seen grabbing coffee in Hader’s hometown of Tulsa, Okla., in December.
In February, a source told People magazine that it seemed as if the pair had "a serious relationship," noting that "they spend a lot of time together."
“They were in L.A. over the Valentine’s Day weekend," the insider said at the time. "On Sunday, they enjoyed a getaway to the Montage Hotel in Laguna Beach. It seems like a fun relationship."
The source also said that Bilson "always seems entertained" when she's with Hader, 42.
“She won’t stop laughing when she’s with Bill,” the source explained to the outlet. “He is very sweet and considerate to her. Quick to open doors and acts very attentive.”
Hader was previously married to writer and director Maggie Carey in 2006. He shares three daughters — Hannah, 10, Harper, 7 and Hayley, 5 — with Carey. The couple announced their separation and filed for divorce in 2017. The divorce was finalized in 2018.
Bilson was previously in a 10-year relationship with actor and “Jumper” co-star Hayden Christensen until they split in 2017. The former couple shares a daughter — Briar Rose, 5 — together.