Willis, 32, wore a black bodysuit in front of a display of posters and a cardboard cutout of the “Keeping Up with the Kardashians” star.
She sported a middle part with her long dark hair and had on glam makeup similar to Kardashian's normal style.
The “Dancing with the Stars” alum channeled the reality star for the one-year anniversary campaign for SKIMS.
“Happy Birthday @skims !!!” Willis wrote in her first post.
She added: “Thank you to the team and the oh so lovely @kimkardashian for including me. You are a gem my dear.”
One fan commented on her disdain about Willis supporting Kardashian.
“Youre [sic] a Rocket but kim is awfull [sic]....in every Part not a good rolemodel,” the user wrote.
Willis defended the reality star and responded, “@kimkardashian is a lovely person and I would ask that you don’t speak unkindly about her.”