Kelly Clarkson always knew it had to be in her blood.Some long-forgotten ancestor, the Grammy-winning North Texan reasoned, had to have been the source of her drive to succeed and her ability to overcome long odds.But until recently, Clarkson knew next to nothing about her family history beyond her grandparents. So, she started investigating with help from Who Do You Think You Are?, the TV series in which celebrities do genealogical searches that often yield surprising and provocative results.Im a very strong presence as a female, and I totally get that from my mother, Clarkson says in the season premiere, which airs at 8 p.m. Tuesday on TLC. Thats why Im interested in this ancestry stuff, because theres got to be a whole line of us. Weve got to get that from someone.Taking over a search that her mother Jeanne had begun online a few years earlier, Clarkson found what she was looking for and then some in the person of Isaiah Rose, her 3x-great-grandfather.Clarkson discovered that, during the Civil War, Isaiah fought for the North, was taken prisoner by Confederate troops and was sent to Andersonville (an infamously brutal POW stockade where one in three inmates died), only to escape his captors.After the war, he returned home and became the sheriff of Marietta, Ohio, and eventually a hard-charging Ohio state senator with a brood of seven children.All of which left Clarkson, the Burleson girl who launched a multiplatinum recording career after winning the first season of American Idol in 2002, quite emotional.We [she and her mother] come from a long line of strugglers, but at the end of the day we survive, said Clarkson after the journey that had her standing over Isaiahs grave in Cole Run, Ohio, and celebrating a life well lived. This was the coolest thing Ive by far done in my life.Of course, Clarkson is one of the lucky ones.As actress Lisa Kudrow, one of the executive producers of Who Do You Think You Are?, points out, About 30 percent of the time, these stories hit dead ends because there are no records or its just 500 years of sheep herders, so theres no story to present.Kudrows own genealogical search during the shows first season was an emotional journey as well.Her trek to Europe involved Kudrows great-grandmother, who she discovered had been killed and burned by Nazis during World War II. But the trip also put her in contact with long-lost Polish relatives with whom she has remained in contact.This is the first season of Who Do You Think You Are? on TLC. The first two seasons, beginning in 2010, aired on NBC.Other celebs showcased in this eight-episode season are Christina Applegate (airing July 30), Chelsea Handler (Aug. 6), Cindy Crawford, Zooey Deschanel, Chris ODonnell, Jim Parsons and Trisha Yearwood.The show is based on a long-running BBC series of the same name, but executive producer Dan Bucatinsky thinks its better suited for America in some ways.If you think about America, every single person comes from some kind of struggle somewhere, he says. You dig back a generation or two, theres something in every uniquely American story where you cant quite believe it.Clarksons search left her feeling way more connected to her roots I could not be more proud of this man, she says in the show and now shes eager to investigate others from her family tree.Im just definitely grateful that thats my past and its cool to find out how far back that strength comes from, she says. I think everybody should do this. Its cool to know your story.