ADEN FLINT is leaving Middlesbrough to join Championship rivals Cardiff City.The centre-half is due to undergo a medical with Cardiff within the next 24 hours, with Boro having agreed a deal for his departure.Cardiff are understood to be paying an initial fee of around £4m, but clauses within the deal means the price for the centre-half could rise to £6m.Flint joined Boro from Bristol City last summer for a price of around £6m, and signed a four-year deal on Teesside.He was a key member of Tony Pulis' first-choice defensive line-up last season, making 39 Championship starts as Boro narrowly missed out on a place in the play-offs.However, he will leave Teesside after just 12 months in the Boro ranks, with Jonathan Woodgate overhauling the squad he inherited from Pulis when he was appointed head coach earlier this summer.