New Aston Villa head coach Dean Smith has been joined at the club by Richard O'Kelly, who was his assistant at Brentford and Walsall.
O'Kelly was confirmed as Villa's new assistant head coach on Monday, with former Chelsea and England captain John Terry already announced as Smith's other assistant.
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Meanwhile, Thomas Frank, who has worked as assistant head coach at Brentford since December 2016, will continue to take first-team training as the Sky Bet Championship club search for a new manager.
Despite losing both Smith and O'Kelly to Villa, Brentford co-director of football Phil Giles says the duo left Griffin Park in amicable circumstances.
He said: "The departure of Dean and Richard happened very quickly but they both left on good terms.
"We understood Dean's desire to take the job at Villa and everyone knows his history at that club. He wanted to take Richard with him and we were able to reach an agreement.
"I would like to take this opportunity to thank them both for all their work at Brentford FC, and look forward to meeting up with them again in future fixtures."
Smith made the decision to leave Brentford - who have received compensation from Villa - to join the club he supports, despite the Bees being eight places better off in the Championship.
His first match will be at home to Swansea City on Saturday.