The Empire star is heading to the Aloha State to sing live with the "Without You" singer during three of her upcoming performance dates, and Smollett had nothing but love for working with the best-selling star, who also makes an appearance on the Fox drama this fall.
"Mariah is just amazing," the 33-year-old actor told ET backstage at the iHeartRadio Music Festival at the T-Mobile Arena in Las Vegas, Nevada on Saturday. "The support that she's shown me so far, she absolutely did not have to be as supportive as she is but she has been."
"It was supposed to be one night only, that sold out in like a couple of hours so they added a second show. That sold out so now we're gonna do three shows!" he added.
Carey shared the news on Twitter on Tuesday, and Smollett retweeted the diva, writing, "I love you. This is crazy. Let's go!!! #SweetSweetFantasy."
But performing with Carey and starring on Empire aren't the only things Smollett has on his plate -- he's also been spending a few early mornings sitting in as a guest co-host alongside Kelly Ripa on Live!
"That honestly is just so much fun," he marveled. "Kelly's become a good friend since I first went on the show like a year and a half ago so it's just fun to play with her."
However, Smollett said he doesn't think there's a permanent future as a long-term co-host on Live! in the cards for him, given the time constraints and pressures of filming his hit Fox drama, in which he stars as singer Jamal Lyon, son of Terrence Howard's Lucious Lyon.
"For me, there's no chance that I would ever be able to do something like that," Smollett said when asked if he would consider signing on as a full-time Live! co-host. "Jamal kind of takes up my time."
"I was sad because I love Kaitlin personally, outside of the show," Smollett shared. "It's always tough when you lose a character."
However, he also teased that it's possible fans might see Doubleday reprise her character in future episodes.
"Empire is known for our flashbacks and good stuff like that," Smollett hinted. "You never know."
In August, Smollett spoke with ET about his Empire musical collaboration with Carey back in season two, recounting how the celebrated songstress "landed at 1 a.m. She came into the studio. We were there until seven in the morning, and we just recorded the song, and it was incredible, and I love her." Check out the video below to hear more.