The couple's 24-year age gap has been the subject of unwanted comments.
The former One Direction star replacing Shia LaBeouf in Don't Worry Darling.
The actor participated in an Instagram fight challenge alongside Drew Barrymore, Halle Berry, Scarlett Johansson and more.
Brad Pitt, Margot Robbie, Joaquin Phoenix and Renée Zellweger are among the stars attending the bash at London's Royal Albert Hall.
The actor received her first Academy Award nomination for her performance in "Little Women."
The actress, 23, pushed back on a comment from someone on Instagram who remarked that the "Scrubs" actor is 44.