The 22-year-old, who can play at centre-back or left-back, is no stranger to manager Paul Tisdale having played against the Grecians during a seven-game loan spell with Aldershot earlier this season.
"We've seen Myles play and there's a lot of potential there," Tisdale said. "So we are excited about the possibility of seeing his development with us.
"We're looking at this with a view to a player that can break through into the first team. So we're excited by his potential as we've identified him as a talented and bright young individual."
City's new number 27 was with Leyton Orient before moving to Aberdeen and he then spent 18 months at Ewood Park without making any appearances before his departure earlier this month.
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