The couple, who met after they starred together in the 2019 play Betrayal, are reported to be engaged, and fuelled rumours further when the actress, 37, was pictured wearing a huge diamond on her ring finger in a photo shared by Strictly Come Dancing's AJ Odudu.
WATCH: Everything you need to know about Tom Hiddleston's career
Zawe looked sublime in a long flowing pink dress but concealed her sparkler on the red carpet by draping her black handbag across her hand.
The two actors have kept their relationship out of the spotlight after meeting on set, only to confirm their romance at the Tony Awards last September.
Meanwhile, Zawe has confessed she no longer intends to work alongside her beau in the foreseeable future. "I've been working with Tom on stage for a year solid – every night – so now we need at least two years apart now," she joked to the Mirror.
Zawe Ashton pictured with a large diamond ring
On the night, the Fresh Meat star revealed how she has been splitting her time between London and LA during the pandemic. Zawe is currently working on a period drama called Mr Malcolm's List where she plays a character living in 1800s England called Julia Thistlewaite.
"I've got into period dramas late - everyone else is over them, but I only want to do them now. They are so freeing," she added.
The couple met back in 2019
Tom, 41, was previously in a very high-profile romance with Taylor Swift in 2016. Speaking about his love life, he once told The Telegraph: "Everyone is entitled to a private life. I love what I do and I dedicate myself with absolute commitment to making great art and great entertainment, and in my mind I don't conflict the two.
"My work is in the public sphere and I have a private life. And those two things are separate."
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