If you grew up listening to Something Corporate and Jack's Mannequin, you probably know the name Andrew McMahon. He's the piano-wielding singer-songwriter who fronted those bands, spawning countless pop-rock emo anthems that his fans still know every word of. Don't believe it? Go to one of his shows, where all those in attendance are belting out track after track as McMahon parades around the stage with his infectious charisma.

He began his musical career at 17. Now 36, he recently released his third album under his solo project, Andrew McMahon in the Wilderness, called Upside Down Flowers.

This week, he wrapped up the Upside Down Flowers Tour -- and invited ET to sit down with him before the show, where we also got an intimate glimpse at his sound check along with a group of about 40 fans.

"This has been amazing, it's been more work than I've ever put into a tour," McMahon tells ET. "This is like two hours top to bottom... we're usually, 'let's go out tonight.' This tour is like I need to go to bed [after a show], you know what I mean?"

"It'll be bittersweet when we pack it up because I think as tough as it's been in that sense, the connection has been really, it's been profound, like a lot of these audiences. It's been cool to be able to play so much new music and so much of the catalog in one spot," he adds. "And seeing how all these songs interact and how these stories kind of, the past informs the present. It has been really cool."

It's amazing that with nine full studio albums under his belt, the songs do all interact. It's hard not to notice the juxtaposition and growth from Punk Rock Princess to Cecilia and the Satellite and Teenage Rockstars.

"I like doing 'Punk Rock Princess' acoustically a lot. For me, it's a little more emotionally connected that way," he says with a laugh. "But it's also just fun, you know, and for the audience who hasn't really gotten to see us play some of those older songs that were, like, very young and, you know, just kind of simple rock, kind of supercharged moments. It felt like a good time to resurrect it and put it in the set list. The chorus is obviously a little bit campy but I still sort of connect to the general sentiment of songs like that, you know, and it was a love song," he says of the 2002 hit. "I was a kid and I legitimately played in this, like, indie rock band in high school and, at the time, the girl that I was interested in, she liked punk music and so there was like, it was almost like a really great metaphor for what was a constant disparity in our relationship, which was like she was cooler than I was and she liked punk and I was this, like, squirrely kid in, like, a piano band."

But McMahon is no longer pining for that Punk Rock Princess. He's happily married to his wife, Kelly, with whom he shares a 5-year-old daughter, Cecilia, and the two often hit the road with him.

"They do, yeah," he shares. "Once Cecilia started preschool last year it was like, she loves being with her friends, so we try not to go more than two weeks. It's kind of the rule... it's a little bit of a juggle right now."

McMahon said his little one "pretty much" demands he play 'Rainy Girl' when she's able to catch a show.

"Anything that references her, she's very pleased to hear for sure," he notes, before acknowledging just how much his life has changed since becoming a dad.

"It's interesting. I think I was more nervous about how it would impact the professional side than I think I needed to be, and in a weird way, if you think about it, 'Cecilia'is the biggest song that I've ever released and I think I didn't realize that becoming a father would actually light a fire to do my best work," he shares. "And also to sort of strip away sort of ancillary things that don't need to fall under the purview of what my day is. I mean, it's not like I'm out shedding friends, but some random interaction that doesn't need to exist or whatever, you know? You make your way home more often because you wanna be there... yeah, a lot has changed."

"I think they are a factor in my process now, you know?" he adds. "Like, with this record, having written so much of the first two [albums] while I was traveling and going out to other places, I was like, I'm gonna try and just do what I used to do which is just be disciplined; I'm gonna sit down and write this record at home, you know?"

"And that became such a beautiful part of the story of Upside Down Flowers, this idea of waking up with my girls and doing breakfast and doing whatever I had to do to help get her off to school and then sitting down and working on music," McMahon continues. "It became this part of my process, like, 'OK, I'll work during the day and then I'll cook for everybody.' So, I'm a little more grounded, although I've had my, you know, I've had that fall away from time to time as well, but yeah, I just think I'm more focused."

McMahon also opened up about playing the Teenage Rockstars video for his former SoCo and Jack's Mannequin bandmates, revealing they were the first to see the final product.

"I made sure they were the first ... and I waited until the video got put together," he explains. "I look at that song as like a total package with the video... that's the presentation of it that I love. So yeah, I sent it out to the guys and everybody was super cool."

"I was a little nervous to send it but I also feel like...it feels very honest to me," he adds. "It doesn't feel like there's a lot of judgment in that song."

McMahon revealed that he started writing the song during the Jack's Mannequin era, but didn't quite have enough perspective until years later to finish it.

He also shared he has thousands of songs he has started that have never seen the light of day.

"I mean, hundreds a year probably, yeah," he notes.

As for what's next? McMahon's also thinking about that. And yes, he's heard the "three theory" (three Something Corporate albums, three Jack's Mannequin albums and three Wilderness albums).

"It's so funny 'cause I've had all these people coming up to me on this tour and being like, 'I heard you're retiring' or 'I heard you're done.' I'm like, 'Where did you hear that?' he says.

"The short answer is, me without writing songs and releasing music and traveling is half of me, so...this is what I do," he continues. "I have no plans to stop recording or not do another Wilderness record."

"What I will say is I definitely feel like I'm in a transition, not necessarily that I'm not gonna do this project or whatever, but I think because there are these three records and I think that all three sort of do -- they speak to each other and they do create a sort of feeling, at least at the moment, a feeling of completion and like, 'OK, what's next?'" McMahon shares. "It's put me in a position where I feel like I'm going home with this, like, fresh outlook and who knows what's next? I wouldn't say it's anything for anybody to be worried about."

He does say he's likely to start on some scoring work.

"Whether it's working on TV and film or writing with other artists for their projects... I think I'll be doing some amount of that, maybe more so than I've done in the past," McMahon points out.

Regardless, expect more music sooner rather than later.

"Truthfully though, I wouldn't be surprised if there was more music soon only because I have Disneyland with my [Cecilia] for her birthday the day after this tour ends and then I'm in the studio for two days as soon as I'm back from that," he says.

And he's also thinking about what his life will look like through the next decade.

"I don't know if it'll be the same cycle [of releasing an album and touring]. It's really hard for me to say," McMahon shares. "I think, in a dream world, I'd be able to sort of plant some flags in other areas of this business as far as being a songwriter who can contribute to other projects."

"I look at guys like Randy Newman," he concludes. "I think there's something really remarkable about guys like David Foster, these guys who can write for themselves, they can write for other people and I like to see it move that direction and then let the touring fall where it falls from there."

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