Before making their grand entrance at the swish event, Rachel's make-up artist shared a snap of them posing together with fans fawning over them.
"How cute! I heard the rumors. Cutest couple," one fan wrote.
"They’re a real couple?! So random but love them both!" another said.
Rachel, 38, and Saturday Night Live alum Bill, 41, were first seen grabbing a coffee together in his hometown of Tulsa, Oklahoma, just before Christmas.
According to Us Weekly, Bill and Rachel were also seen out on a date in early November suggesting that they have been seeing each other for a number of months.
Bill was married to writer/director Maggie Carey for 11 years, and they split in 2017.
Rachel has one child, Briar Rose, who she shares with ex-partner Hayden Christensen.