Academy coach Willie McStay has left his role at relegated Bristol City.
The 51-year-old Scot spent a year at Ashton Gate, having been appointed during Derek McInnes' spell as manager.
McStay is the latest departure from City's backroom as head coach Sean O'Driscoll looks to restructure following their drop to League One.
goalkeeping coach Nigel Spink and strength and conditioning coach Alan Hughes have all recently left the club.
has been drafted in to replace O'Kelly, while former Cardiff keeper Lee Kendall has taken over from Spink.
Keith Burt has also been brought in
as director of football.
Speaking about McStay's exit, managing director Jon Lansdown said: "Willie has played a big part in building our under-21 squad and has helped a number of those players progress into the first team.
"I'd like to thank him personally for his contribution and wish him all the best for the future."