The pair, Jack and Tyler, chose City’s academy over United’s when they were signed at the age of 10.
Tyler represents Scotland at U16 level, while Jack opted for the nation of his birth to play for England.
The 16-year-olds are highly-rated prospects and they had been tipped for a future in the first team at the Etihad.
However, Darren, who is a Technical Director at Old Trafford, wanted his sons to play for United.
According to widespread reports, the pair have opted to join United and the Red Devils will pay a compensation fee of around £1.25m for the duo.
City are thought to be angered by the arrangement, and have in turn secured a deal to sign United youngster Harrison Parker.
United have denied speculation that the fee they’re paying for the 16-year-olds is a record of its kind.
The duo won’t be able to sign professional terms until their 17th birthdays, which is next March.
Fletcher played over 300 times for United’s first team, winning ten major trophies.
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