The 50-year-old actor kicked off his "The Man. The Music. The Show." tour at the SSE Hydro in Scotland, and delighted fans with performances of songs from "The Greatest Showman", "The Boy From Oz" and "Les Miserables", among others.
After Hugh recalled the moment Keala sang "This Is Me" - her spine-chilling number from "The Greatest Showman" - to movie bosses, he stunned the arena by introducing the actress to perform the uplifting tune.
Fans were quick to praise the 43-year-old after the performance, with one writing on Twitter, "Genuinely cried when Keala started singing - I would've paid the ticket price to see her alone, no joke."
Another added, "Thank you to the amazing @kealasettle for coming to Glasgow to sing such a powerful song that means so much to so many. I think the dream of seeing that song performed by the beautiful Keala, came true for many last night."
A third hilariously tweeted, "@kealasettle thanks for giving us the biggest surprise last night! Thankfully my heavily pregnant wife managed to control the excitement - it could have led to us calling a baby Hugh/Keala!"
Following the show, Keala shared a picture of herself and Hugh hugging backstage on her Instagram page, and wrote, "You did it, my brother @thehughjackman. Thank you so much Glasgow for an incredible opening night. #ssehydro #themanthemusictheshow."
Keala also confirmed she will be joining Hugh in Glasgow on Wednesday and Thursday night. It remains to be seen whether or not Keala joins the actor when the tour moves venue.