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Chadwick Boseman posted the video to his Instagram. @chadwickboseman Instagram/Walt Disney Studios Motion Pictures

"Black Panther" star Chadwick Boseman died of cancer on Friday. He was 43.

Boseman was diagnosed with colon cancer four years ago, his family said in a statement, according to the Associated Press. He never spoke publicly about his illness.

Months earlier, fans of Boseman expressed their concern after the actor appeared to have lost weight in a video he posted to Instagram.

Boseman was speaking about Operation 42, an initiative that aims to help hospitals that serve African-American communities during the coronavirus pandemic.

However, almost all of the comments were focused on Boseman's appearance, with many users expressing shock, commenting that he looked "thin," and asking: "Are you ok?"

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"Black Panther" star Chadwick Boseman died of cancer on Friday. He was 43.

Boseman was diagnosed with colon cancer four years ago, his family said in a statement, according to the Associated Press. He never spoke publicly about his illness.

Just three months earlier, fans of Boseman expressed their concern after the actor appeared to have lost weight in a video he posted to Instagram.

Boseman was speaking about an initiative called Operation 42, which aims to help hospitals that serve African-American communities during the coronavirus pandemic.

The project, which he is partnering with Thomas Tull on, will honor baseball legend Jackie Robinson, who Boseman played in the biopic "42."

In his caption for the video, Boseman wrote: "I am hearing stories of desperation from people all over the country, and we know our communities are suffering the most and urgently need help. Celebrating #JackieRobinsonDay with the launch of Thomas Tull's #Operation42, a donation of $4.2 million in personal protective equipment (PPE) to hospitals that service the African American Communities who have been hit the hardest by the Covid-19 pandemic.

"Thank you, Jackie, for refusing to accept the world as it is, for showing us that we can make a difference."

Despite his message, comments on the video were focused on Boseman's apparent weight loss, with many users expressing shock at his appearance, commenting that he looked "thin," and asking: "Are you ok?"

Several fans also asked whether he was losing weight for an upcoming film role.

Representatives for Boseman did not respond to Insider's request for comment on the reactions to the video in April.

Boseman has several upcoming film roles on his IMDB page, including "Black Panther II," "Yasuke," in which he plays an African samurai, and Spike Lee's "Da 5 Bloods," in which he plays a Vietnam war veteran.

He is also appearing in "Ma Rainey's Black Bottom," a biopic about the "mother of blues" starring Viola Davis.

Boseman is known for being incredible shape in past movies, thanks to his dedication to strict training programmes that helped him gain the physique he showed off "Black Panther" and "Avengers: Infinity War."

Boseman is a student of martial arts, too, and a martial arts expert helped him train for "Black Panther," while Marvel's decision to shoot "Infinity War" and "Endgame" back to back, right after filming for "Black Panther" had finished, meant that Boseman spent a year in constant training.

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