Mulligan made her hosting debut on Saturday (10 April).
As is customary, she delivered the opening monologue, telling the audience: “I spent the last year quarantining in the English countryside with my husband and my two small children, which is the beginning of most horror movies.”
While she said her husband was at home taking care of their children, Mumford soon stood up, revealing his presence in the audience.
The pair were childhood pen pals and married in 2012.
“Do you know if they booked a musical guest for tonight?” Mumford, the lead singer of Mumford & Sons, asked her.
When Mulligan assured him that yes, a musical guest (Kid Cudi) was already lined up, Mumford humorously insisted: “If they end up needing anyone I’m very happy to do it.”
He then started playing his guitar, much to Mulligan’s apparent surprise.
“I thought you were giving me the signal,” he explained. When Mulligan questioned him about this alleged signal, he added: ““Our secret couple signal for ‘Play the guitar.’”
The actor reacted in faux bewilderment, but Mumford wasn’t discouraged, and ended up joining her onstage for the rest of her monologue.
Mulligan is currently up for the Academy Award for Best Actress for her role in Promising Young Woman. The ceremony will take place on 25 April.