Coolio died Wednesday after a suspected cardiac arrest. He was 59.
ET's Kevin Frazier spoke with Mitchell about Coolio crafting the theme song for his and Kenan Thompson's Nickelodeon show, Kenan & Kel, and the way he found out about the "Gangsta's Paradise" rapper's death.
"I was here at the house with the kids, and I was on social media, and I saw under someone else's page like, 'Oh yeah, RIP Coolio,' and I'm like 'Wait, wait, wait,'" Mitchell explained. "I said, 'Hold on,' and then I started looking around and saw it was true."
He continued, "Then my phone started blowing up, and everybody hit me up about it."
Coolio -- who was born Artis Leon Ivey Jr. -- died in Los Angeles Wednesday at the age of 59. His longtime manager, Jarez, confirmed the news to TMZ. Jarez told the outlet that paramedics suspected cardiac arrest was the cause of death, though no official determination has been made.
Mitchell's friendship with Coolio was decades long, with the pair first meeting on the set of All That.
"Awesome," Mitchell said of the first time he met the late rapper. "One thing I say about Coolio and my experience with him all the time, is that he was always a great time. Always had a smile on his face, always cracking a joke. First time I met him was on All That, I believe it was our first season, and he was in a Good Burger sketch, and his comedic timing was so amazing."
"Also, a great actor," he added. "And then after that, he performed on the show."
Mitchell, who used to rap as well, said Coolio once brought him onstage during a performance to freestyle with him.
"He brought me up onstage, and you gotta imagine that, like, this is my first show, first season, and then Coolio, who's like an amazing rapper on the radio at that time, brings me onstage to freestyle with him," Mitchell recalled. "[This] was such a big moment for me, 'cause I was a fan, you know what I mean?"
Not long after, Coolio went on to craft the theme song for Kenan & Kel, something that came naturally after building a friendship with Mitchell and the producers and writers at All That.
"A lot of the entertainers that would come on All That, ended up hanging out with us, and staying friends with the producers and the writers, which was super awesome, and when we did the spinoff, and him doing the Kenan & Kel theme song, that was awesome," Mitchell gushed.
"I mean, I remember him telling Big Boy's Neighborhood on the radio out here, that we were gonna be shooting at Universal CityWalk, and I mean, everybody was there. I'm talking all of Los Angeles. It was a big party. That's what people can see on the other side of the camera, that's why you see the energy is so high," he continued. "It was just such an awesome moment, and that song still goes, like, people play it in the clubs, and play it everywhere, and it says a lot to his lyrics."
They stayed in contact too, remaining friends long after Mitchell's days on All That and Kenan & Kel. In fact, the Sam & Cat actor revealed that he had even spoken to Coolio just a few months ago.
"I was doing a project for iHeart, and I reached out to Coolio, told him to come on, and we were able to talk," Mitchell shared. "He was in the U.K., I knew it was very, very early, but he agreed to do it, which was super awesome, and we just had a real conversation which was so awesome.
"I remember at the end of the conversation, he told me, 'Now you know it's early out here in the U.K., I'm on tour, but when I heard that you were doing this, I had to come and talk to you, and I just love the positivity that you always have and I want you to keep that positivity and the positive projects, and the things that you do and making the choice,' and I said, 'Yo, I will. I definitely will do that,'" he added. "But it's just such a beautiful thing, like, he's like a big bro since I was a kid, now I'm an adult, and still giving great advice, like he does in his lyrics as well."
As far as what Coolio's legacy will be, Mitchell said it's multi-faceted -- from his music and his iconic hair and style, to what he's done for Black culture and hip-hop.
"You have to mention Coolio if you're talking about hip-hop, if you're talking about music in general," Mitchell insisted. "Things that he did on the platforms as far as like movie soundtracks, the style, his hair -- an icon, just a fashion icon. I don't think anybody else did it as good as him after that. You just gotta give it up to Coolio for what he did to the culture, and what he did for hip-hop."
Mitchell added, "I just want people to know how good of a person he was, and his music, and just what you saw on television and in the music, he was that offline too. Just a great guy."