Kate Upton Celebrates 21st Birthday: A Look At The Sports Illustrated Model's Sexiest Looks [PHOTOS]

Supermodel Kate Upton finally turning 21 years old on Monday, after making tongues wag ever since her infamous Cat Daddy video with famed photographer Terry Richardson. Wearing just a tiny bikini, she danced to music by the Rej3ctz in the video that quickly went viral. Afterward, she landed her first Sports Illustrated cover at just 19 years old.

Upton has since had quite a busy career, landing on the cover of Sports Illustrated magazine again at the age of 20, being featured on Maxims’s Hot 100 list and being labeled the "sexiest supermodel on Earth" by Vogue.

Her next career move shows off her acting skills, as she is staring in the upcoming film “The Other Woman.” While it is unclear what her exact role is, the comedy also features stars Cameron Diaz, Taylor Kinney, Nicki Minaj and "Knocked Up" actress Leslie Mann. The comedy is scheduled to be released April 25, 2014. Check out Upton's hottest looks: