"I'm excited! My baby sister [is] getting married [and] it's gonna be special to have the whole family there. We're gonna have a great time!" Derek shared with ET's Lauren Zima at the Los Angeles debut of Travis Wall and Shaping Sound's new show, After the Curtain, at Royce Hall at UCLA on Tuesday.
"It's gonna be like, a week-long event," he added. "It's gonna be amazing."
"I think I will be making a little speech," the 32-year-old dancer admitted. "There's always surprises with my family that aren't planned, so there [will be] plenty of surprises."
As it so happens, Julianne's wedding is going down on the same day her DWTS co-stars, Maks Chmerkovskiy and Peta Murgatroyd, are set to tie the knot! But according to Derek, it's not going to cause too much conflict.
"We have different friends [and] different groups," he explained.
Outside of his sister's wedding, Derek already has a lot on his plate. From a sold-out live tour that just wrapped -- which saw him and his sister perform 55 shows in 48 different cities in less than two months -- to his new NBC series, World of Dance, which has been delivering stellar ratings, the performer has been working harder than ever in recent months. -- which That's why he says it's unlikely he'll be returning to DWTS "in the near future."
"I've got a lot of other new projects happening right now. I'm very excited," he explained.
But, while Derek said he's enjoying this "new chapter" in his life, he didn't close the door on the idea completely, sharing, "I love Dancing With the Stars. It's my family, so who knows?"
With his heavy workload keeping him on the road and away from his girlfriend, Haley Erbert, Derek said he's been relying on the magic of digital communication to keep their relationship going strong.
"That's like, the beauty of technology, you know? You've got FaceTime, you've got all sorts of things," he explained. "But I'm gonna be seeing her very soon now for a whole week so, it's good."
The cute couple have gotten more and more open with their relationship in recent months, and Derek said that being in a public relationship has been a new experience for him.
"It's unusual for me. I'm actually pretty private," he shared. "But yeah, it feels good though."