E! News said the 40-year-old actress and 51-year-old singer and actor walked the red carpet separately before posing for photos together inside the event.
Holmes wore a purple Zac Posen gown with 300 yards of hand-sewn tulle, according to People. Foxx sported a black suit with a sequin panther pin and purple shoes, which matched Holmes' dress.
"Jamie Foxx matching his shoes to Katie Holmes. A couple!" one fan wrote Monday on Twitter.
"why are jamie foxx and katie holmes so lowkey??? they clearly came together last night," another added Tuesday.
Holmes and Foxx have been linked for years but have yet to publicly confirm their relationship. Holmes was previously married to Tom Cruise and is parent to daughter Suri with the actor, while Foxx is dad to daughters Corinne and Annalise.
"They still plan to keep their relationship private," a source told E! News in April 2018. "This is what has worked for them and what they're comfortable with."
Holmes and Foxx celebrated the actress' 40th birthday together in December. The pair stepped out for dessert with Holmes' mom, Kathleen Stothers-Holmes, in New York.
"Katie and Jamie looked happy. They both came in the same car together, with her mom," an insider told Us Weekly. "[They] all seemed like they were having a great time."