It's the second time in a row that Fletcher has presided over a movie about an icon of 1980s British pop culture.
Bohemian Rhapsody is still expected to hit theaters on December 25, 2018.
Singer was originally hired to direct the film, but after several months of filming, he was let go by producers on Monday (11Dec17) after he reportedly failed to return to the set in the United Kingdom after America's Thanksgiving break.
It is believed that there are about two weeks' worth of shooting left, unless he decides to reshoot scenes, and it remains unknown what the director credit on the final film will be.
Not Bryan Singer, but Dexter Fletcher will now direct Queen frontman Freddie Mercury's biopic "Bohemian Rhapsody". His no-shows resulted in cinematographer Thomas Newton Sigel having to step in to helm some of the days while Singer was absent.
Production had been halted after Singer failed to return to the set after Thanksgiving.
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Singer, however, accused Fox of not letting him have time off the project to deal with health issues for one of his parents.
"I needed to temporarily put my health, and the health of my loved ones first", Singer said in a statement, The Wrap reported.
'Unfortunately, the studio was unwilling to accommodate me and terminated my services, ' he continued.
Filming has been taking place in the United Kingdom, with Ben Hardy, Joe Mazzello and Gwilym Lee starring as Queen's other members.
Fletcher's directing credits include "Eddie the Eagle", distributed by Fox, and "Sunshine on Leith".