Katherine Evelyn Anita Cassidy was born in Los Angeles, CA. Her father, David Cassidy, was a pop star who rose to superstardom in the early 1970s with the hit song "I Think I Love You" and for playing teen poster boy Keith Partridge on "The Partridge Family." Her mother, Sherry was a high fashion model who retired to raise her children. Cassidy's family was also a "Who's Who" of Hollywood names. Her grandfather Jack was a Tony Award-winning musical actor before his 1976 death in a house fire, her grandmother Evelyn Ward was an actress, and her uncles Shaun, Ryan, and Patrick were also pop stars and actors. Cassidy's other grandmother Shirley Jones, who married her grandfather Jack in 1956, played Shirley Partridge alongside her real-life stepson, David, on the pop phenomenon, "The Partridge Family." Cassidy began entertaining as soon as she was able to walk. Her family put her in various classes as a child, including piano, guitar, singing, dancing, and acting lessons. She was also a gymnast and cheerleader. The future star attended Calabasas High School, where she began her acting career. At the suggestion of her mother, Cassidy started modeling and acting in local theater productions prior to her high school graduation in 2005. Viewers were first exposed to Cassidy in the documentary "Bubblegum Babylon" (VH1, 2002), about the rise and fall of teen idols. The camera crew followed Cassidy while she recorded her father's hit song "I Think I Love You" to jumpstart her singing career. Her father, however, was disappointed that Cassidy did not wait for her career to take off before recording his classic tune and publicly criticized her decision on the show. Undaunted, Cassidy signed with Artemis Records, where she met the pop group, Dream Street. One of the band members, Jesse McCartney, went on to become a hit solo singer in the mid-2000s. The pair began dating after Cassidy appeared in McCartney's music video for "She's No You" in 2005. While her boyfriend graced the covers of teen magazines, Cassidy modeled in advertisements for clothing brands such as Abercrombie and Fitch, and Rock & Republic. Cassidy dated the pop star for three years, even inspiring the Leona Lewis song "Bleeding Love," which McCartney co-wrote. The couple ended their relationship in 2008 while the track became iTunes' top-selling song that same year.Cassidy's acting career blossomed in 2005 after she booked guest roles on several TV series including "The Division" (Lifetime, 2001-04), "Listen Up" (CBS, 2004-05), and "Sex, Love & Secrets" (UPN, 2005). But it was a recurring role in the long-running drama series "7th Heaven" that showcased the actress' ability to connect with viewers. As the Camden family's sneaky friend Zoe, Cassidy appeared in a four-episode arc on the show, beginning with the episode titled "The Fine Art of Parenting" that first aired in January 2005. The actress graduated to feature films in 2006, starring in a handful of big screen projects. Cassidy acted alongside Camilla Belle in the thriller "When a Stranger Calls," about a teen babysitter stalked and harassed by a vicious prank caller. Special effects and a hilarious costume gave the actress oversized breasts when she played Samantha, the grown-up daughter of Adam Sandler's character in the comedy, "Click." Cassidy appeared in her second horror film that year when she played a sorority girl terrorized by an escaped maniac in "Black Christmas." The holiday-themed blood fest also starred Michelle Trachtenberg and Lacey Chabert. With a string of television appearances and feature films to her credit, Cassidy reportedly beat out pop singer/actress Jessica Simpson and reality TV personality Kristin Cavallari for a role in the big screen adaptation of "Dallas" (CBS, 1978-1991). The remake of the cult TV series was rumored to star John Travolta as oil tycoon J.R. Ewing and Jennifer Lopez as his wife and former beauty queen, Sue Ellen. Cassidy was reportedly cast as Lucy Ewing, a problematic teenager and one of the heirs of the family's business. The "Dallas" remake stalled early on in its production stage and by 2009 had yet to confirm any actors officially on board for the film.Cassidy returned to the small screen in 2007 with a six-episode arc on "Supernatural" as Ruby, a demon who guides Jensen Ackles and Jared Padalecki's characters in the horror series. Genevieve Cortese replaced Cassidy as Ruby in 2008 due to budgetary reasons, but the hardworking actress already had her next project lined up. She next played the bride Trish Wellington on "Harper's Island" (CBS, 2009), a 13-episode series about members of a wedding party who mysteriously start getting murdered. The show's plot, including the identity of the killer, was so secretive that even the actors were kept out of the dark when it came to the script. Cassidy told the press that filming "Harper's Island" was very much like being on the reality hit, "Survivor" (CBS, 2000-). Plenty of mystery and intrigue followed Cassidy when she signed on to play Ella Sims, an ambitious and seductive bisexual woman living in "Melrose Place." A remake of the addictive cult soap "Melrose Place" (Fox, 1992-99), the show featured a new generation of young professionals living in the same Los Angeles apartment complex, each with one with their own dark secrets. The series that launched the careers of stars such as Courtney Thorne-Smith and the comeback of Heather Locklear created plenty of buzz for Cassidy and her cast mates when its remake premiered in September 2009. That same year, the actress starred in the feature film "Fencewalker," a mystery/drama written and directed by "The X-Files" creator, Chris Carter. In 2010, Cassidy joined the cast of "A Nightmare on Elm Street," a remake of the horror classic from director Samuel Bayer. She starred opposite Jackie Earle Haley, who took on the role of iconic slasher Freddy Krueger.