Boseman, who played the lead role of T'Challa in the 2018 superhero, passed away in 2020 after a private colon cancer battle.
Speaking on The Graham Norton Show, airing 4 November, Duke reveals: “Visiting [Chadwick's] grave to say goodbye formally and ask his blessing was really great to help deal with it because it was such a surprise – none of us knew that he was sick and we were only weeks away from shooting when we heard of his passing."
British actor Michaela Coel, a newcomer to the Marvel Cinematic Universe who hadn't previously worked with the late actor, says visiting Boseman's resting place helped bring perspective to the film's themes of grief and loss.
"For me visiting the graveside allowed me to not just see Chadwick from a Marvel perspective," the I May Destroy You star explains, "but to understand this was a friend to this cast and it was a real human loss.”
Rather than recasting the role of King T'Challa, who also appeared in Captain America: Civil War and Avengers: Infinity War and Endgame, the Black Panther sequel will address his death and sees the Kingdom of Wakanda tackling a new underwater threat.
"The movie is deeply about grief and how hard and messy it is," Duke — who plays M'Baku — adds, "there is no pretty perfect way through it, and you are changed for ever by it.”
Read more: Every upcoming MCU movie and TV show
Duke adds that his character has a more central role in the sequel, and that he took inspiration from a surprising place.
“I’m doing a lot more [in Wakanda Forever] – a lot more noise and a lot more humour.
"I was inspired by Brian Blessed. I loved him in Flash Gordon – his character’s function is so like mine and I liked how he did it.”
The Graham Norton Show, airs on BBC One, Friday 4 November, at 10.40pm. Black Panther: Wakanda Forever releases in cinemas and IMAX on 11 November.
Watch a trailer below.