Unfortunately, some American Idol alums fade into obscurity, but there are a notable few who become Smash hits. This is especially true of Katharine McPhee and Jennifer Hudson. The second season of Smash premieres tonight, and the two American Idol alums are sharing the spotlight -- Kat as a crafty show veteran, and Jennifer has a newcomer to the show.

When ET Online went behind the scenes of the Smash Season 2 premiere, they asked Katharine what she thought of Jennifer joining the star-studded cast, and she raved about what she brought to the table.

“I think it’s fantastic having Jennifer here,” Kat told ET. “She kind of fills a void that the show didn’t necessarily have...she’s got that incredible voice.”

As for Jennifer, she can’t seem to believe the breakneck pace the show keeps, saying, “It’s like hopping on the express lane on the expressway.” That doesn’t mean she doesn’t like it, however. In fact, it’s just the opposite.

“I’m loving it,” the Weight Watchers spokesperson told ET. “I’m having fun.”

Don’t expect the two to be rehashing their stints on American Idol, though. In an interview with NBC Bay Area, Katharine said, “It never came up, no! We just were there for something entirely separate from where we started, and it’s not a natural thing that you’d think would just come up in conversation.”

It’s not surprising that it was all business. In fact, the one thing Kat told RyanSeacrest.com that impressed her most was Jennifer’s professionalism.

“She is so incredibly professional. I think it’s amazing when people come in for a couple days here and there and they’re just super focused and here is somebody who has achieved so much and she just wants to do such a great job with everything she does.”

Will you be watching tonight’s Smash premiere? Which Idol alum are you most excited to see?

Sources: ET Online, NBC, RyanSeacrest.com