Kit Harington has joined the MCU in Marvel’s Eternals as a character named Dane Whitman.
Announced at D23 Expo, Kit Harington, following reports of his possible MCU arrival just ahead of D23, will play Whitman, a non-Eternal character in the film and yet one who may have some comics heritage. Dane Whitman is also the name of a character known as the Black Knight. He was in fact the third character to bear the moniker. He was featured in a Black Knight solo series following Marvel’s All-New, All-Different Marvel initiative. Marvel did not confirm his character will in fact become Black Knight during the film, instead only introducing him by his pedestrian name.
Source: IGN.com Kit Harington Cast in Marvel's Eternals