The 21-year-old winger is Monk's second summer signing.BCFC
The 21-year-old winger is Monk's second summer signing.
England Under-20 international Mahoney began his senior career with Accrington Stanley before making the switch to Blackburn in 2013.
During a four-year spell at Ewood Park, the England Under-20 international made 21 senior appearances, before leaving the Lancashire outfit in the summer of 2017 following their relegation to League One.
His services were then secured by Eddie Howe's Premier League Bournemouth, who were ordered to pay £425,000 compensation to Rovers because he was under 23 years of age.
Mahoney made two FA Cup appearances during his debut season for the Cherries before joining Championship side Barnsley during the second half of the 2017/18 campaign.
The player will wear the number seven shirt at Blues.