The 29-year-old dancer stopped by ET's Los Angeles studio on Tuesday, where she revealed she'll be making an appearance on season two of World of Dance.
"I actually just did a mentor session with [Derek]. He asked me to come and mentor, so, yeah. I just did it the other day," she told ET's Katie Krause of her involvement with the NBC show, which returns Tuesday, May 29 at 10 p.m. ET. "It was so much fun and the dancers are incredible."
Julianne said the experience was especially "cool" because she was able to reunite with some of the talented dancers that were featured on her and Derek's Move -- Beyond -- Live on Tour show that kicked off in 2016.
"There's actually a couple of people that were on our tour that are now doing [World of Dance]," she explained. "It's so amazing when you can see people that you've worked with [before] and just see them grow and, like, blossom into these incredible dancers or whoever they want to become. There's like a proud mama feeling; 'Oh, you were such a baby, and look at you now!' It's so awesome."
Derek is returning as a judge for the dance competition series, along with Jennifer Lopez and Neyo, with Jenna Dewan Tatum as host. Julianne told us it's been a lot of fun working with her brother on a TV show again (the two previously worked alongside each other on Dancing With the Stars), especially because their creative minds mesh so perfectly.
"Derek's amazing," she gushed. "He's so creative and has this chaotic mind that goes like 100 mph, and I get his language, so I can be his translator sometimes. He's so so brilliant [and] we also just feed off of each other ... we're a good blend and a [good] mix."
But despite the fact that they make a good team now, Julianne admitted that, growing up, it wasn't always that way.
"When we were little, competing, I always wanted to beat him, because I'm his baby sister," she joked. "I remember I beat him a couple times and would never let him live it down. But you know what? Being in an industry, whatever industry you're in, if you have somebody that is that close to you? I mean, the wave and the ride of the ups and downs, relationships and this... to have somebody that close, that's like in the same world as you, that understands it... we've both been very, very lucky to be each other's support. He's rad. I love him."
Julianne also confirmed that she will not be back as a dancer or a judge for Dancing With the Stars' upcoming all-athletes season, premiering April 30 at 8 p.m. ET on ABC. The former mirrorball champion and longtime judge left the show last season to work on other projects and focus on her acting career. She told ET that she actually has another TV series in the works, a fictional ballroom project called Blackpool that's kind of a mix of "Black Swan, I, Tonya and Moulin Rouge."
"So many things are happening," she explained. "Obviously, Dancing has always been my family. I was on it, I left for a little while, I came back. So, who knows what will transpire [in the future]. But as of right now, I'm focusing on that show [Blackpool], my acting and then my music. That's really sort of my focus right now."
Music has always been a passion for Julianne, who told ET that she just started brainstorming music ideas in the last couple weeks, and has already started a little bit of writing while "figuring out the sound."
"I've just been like, 'Wow.' A lot of people ask me all the time, 'What do you like more, dancing, singing or acting?' and I've always said they fulfill something different," she said. "I almost feel like, because I haven't been doing my music, it's almost trickled down to the other, to my acting and dancing. So, I'm like, 'Oh, I need to do it all. It feeds my soul.'"
Though Julianne is still "trying to figure out" exactly what she wants to do, she played coy when we asked her if an album is in the works.
"I mean, who knows," she said. "The way music is now, you can put out one single, you can put out a music video, you can put out an album -- whatever you want to do. But i just want to create music the way that it moves my soul. [I'm] not trying to do it for anyone else, just for the pure creation."
During our interview, the newly red-headed beauty also opened up about her longtime battle with endometriosis in support of the "SpeakENDO" campaign, which encourages women to speak up about their symptoms and help each other out. Julianne told us that while filming shows like DWTS and WoD, she often has "episodes" on set where she has to take a break from the pain.
"I [announced] that I had endometriosis back in 2008," she explained. "With me, I am a tough cookie and I'm just gonna keep going. Laser focus. But [when first diagnosed] I felt like I was sort of in this alone, and people didn't understand, even I didn't understand, the amount of pain I was in."
"I'd be on set," she continued, "and be like, 'Whaaa,' totally hunched over, can't speak. I'm like breathing and [people] will be like, 'What's going on?' In the past I'd be like, 'It's OK, it's OK. I'm fine.' But now, I'm like, 'It's my endometriosis,' and they're like, 'Oh, OK, we'll take five minutes, it's totally fine.' Whereas before, I felt like I just had to push through it."
Of course, she doesn't let the disorder stop her from living her best life. Julianne told us that ever since she tied the knot with Brooks Laich last July, she's felt more "grounded," more "in my body." Which is one of the reasons that led her to dye her hair red!
"I feel like I was a born a redhead," she gushed. "I felt that my whole life. For six years, anytime I would see a redhead I would grab their head and put [their hair] over my head. 'Does it work?'"
"Oh, heck yeah! Oh my gosh, you don't understand -- Ariel's my favorite," she marveled. "I mean, yeah. I would freak out. I would love that."
Press play on the video below to hear what else she had to say about the idea!