Reality TV fans know that the real magic of Dancing with the Stars isn’t the celebrities or the dances—it’s the pairings. But matching a celebrity contestant with a pro dancer isn’t as easy as you might think. In fact, the freshly announced DWTS season 34 pairings looked extremely different just a few weeks ago.

“It’s ever-changing, and there were some pairings that were different three weeks ago,” co-host Alfonso Ribeiro told Us Weekly. According to Alfonso, who himself won season 19 of the ballroom competition show, producers start matching up pros and celebs as soon as they start casting. “Typically, once we have a list of the pros that are gonna be on, we then, at some point, we’ll get the opportunity to hear who’s gonna be [on the show]. But it’s never final, right?” he explained.

However, DWTS casting is famously chaotic—season 33 competitor Jenn Tran found out the night before the official announcement that she would be joining the show—and as more celebs come in, pairings are re-assessed. “Things continue to evolve as new people come in, and you realize, ‘Oh, actually, this is a better pairing than that pairing,’” Alfonso continued. “And they work on it right up until the final day—until [the stars and pros] meet each other.”

Pairings are also approved on a rolling basis, meaning that celebrities cast last-minute have less rehearsal time before the show. This season, that disadvantage has unfortunately been bestowed onto Lauren Jauregui, who found out she was competing on the show with pro Brandon Armstrong just days before the cast reveal on Wednesday. “I actually learned that I was going to be on the show two days ago,” she told Good Morning America. “So I haven’t unfortunately gotten to get in [the studio] with Brandon yet, but we’re gonna get there.”