His contract is due to expire in the summer.BCFC
The 28-year-old returns to a Scotland for a second spell season, having spent the first half of the 2018/19 campaign at Kilmarnock where he made 16 appearances and scored eight goals.
Aberdeen, who are managed by Derek McInnes, are currently fourth in the Scottish Premiership, a place behind Kilmarnock.
Stewart has been a Blues player since August 2016 after moving south of the border from Dundee, but has not figured for the Club since April 2017.
His contract is due to expire in the summer.