Smith's former rap partner said the actor was just as down-to-earth now as when he first recorded music with him.
"He's the biggest movie star on the planet, [but] he's still the same Will - the same good guy," Jeff told People.
"He's just a little harder to get in touch with."
When asked about Smith's marriage to Jada Pinkett Smith, he replied: "He's a hard worker. Will works like that at everything.
"You got to put in hard work to make relationships work and that's what he does with Jada."
Smith and Jeff recorded five studio albums together between 1987 and 1993, including Code Red, Homebase and Rock The House.