"It was so emotional, honestly, because you remember your life before everything happened," Brooke explained to ET while at a surprise event at a Los Angeles high school. "And then fast forward during the years of [Fifth Harmony], experience and stuff, and then now, it's amazing. Sometimes when I'm writing, I put my mind back to that time and I'm like, 'Whoa! OK, get out of it, get out of it, you're not there anymore!'"
"There have been moments where I've definitely teared up writing because there's been so many amazing things that have happened, and so many hard times that I've experienced and hurdles I've had to get through," she continued. "But it's all so exciting for me to put that to pen and paper and make everything my own and in my words. Ultimately, I hope to uplift people through my story."
Brooke also hopes that her readers "feel like they're going through what I'm going through, all the good and the bad."
"Ultimately, I want to just portray my story to the world," she stated. "I feel like people know, but they don't really know me and they don't know me before the group and its success, and why I am who I am. That's going to be really, really important. I touch on everything about my life."
Meanwhile, in the spirit of the holidays, Brooke also spent time with the next generation of artists when she made a surprise appearance at a local Los Angeles high school. The pop star joined StubHub and Mr. Holland's Opus Foundation to donate $77,000 worth of instruments to San Fernando High School last Friday.
The day was extra special for Brooke, who performed her original songs at the school years before she made it big with Fifth Harmony.
"Music is so important to everybody, and especially kids," she expressed. "For me, that was my favorite part of going to school and it still is my favorite part. So to be able to instill that in kids and be able to encourage them to play an instrument and learn to be a part of some musical thing is just incredible. I'm so happy to be a part of it."
The "Perfect" singer also added that "it's imperative" for kids to have a musical outlet. "This really shapes you and it shapes your creativity, and you're able to learn and experiment and try something new… For the kids to actually have an outlet and be encouraged to do so is something that's so incredible. You never know, you could see the next John Legend come out of here."
As for her own musical endeavors, Brooke is working on her solo debut album. "I just can't wait to get the music out," she excitedly relayed, adding that she hopes to tour, release the LP, and maybe get the opportunity to act in the new year.
"I'm just so excited about the music and so focused," she shared. "As far as my album, I know right now we've been recording a lot of songs, so we're figuring out everything for the album. It's coming together. We'll see when it comes out, but I'm really excited for my solo Ally Brooke music to come, my single! [The single], it's going to come out soon. You'll have to wait and see! I'm so excited!"
For more on Brooke's life and career, watch below.