[artist id="2389485"]Taylor Swift[/artist] may consider her tourmate [artist id="2385935"]Kellie Pickler[/artist] one of her BFFs, but Pickler thinks of the 19-year-old superstar, who [article id="1606856"]she'll be hitting the road with[/article] starting Thursday (April 23) in Evansville, Indiana, as her "little sister."

"She's like a little sister to me," the "American Idol" alum told MTV News. "She's a lot taller than me, but like a little sister."

The 22-year-old describes the tour as "amazing," but didn't want to reveal too much about what fans can expect from the girls who collaborated on [article id="1608913"]Pickler's "Best Days of Your Life."[/article] "I can't give away all the secrets, but it is going to be amazing," she said. "It's going to be unlike any other country tour that anyone's ever done."

With a promise like that, it comes as no surprise that the two country stars were able to do the near-impossible and sell out New York's Madison Square Garden without even breaking a sweat. "We're actually going to be back in New York. We sold out Madison Square Garden in, like, one minute," Pickler said. "It's insane. It's going to be a great year. We're excited. We actually just started tour rehearsals. It's going to be a big show."

The girls, who will be on the road through October, aren't new to touring with one another -- but this time, it's all about the girl power. "It's so amazing, 'cause Taylor and I kind of started about the same time and we did our first big country tour two years ago with Brad Paisley," she recalled. "We opened for him and that's really where we got to bond and get to know each other."