Promoted Championship side Watford have signed centre-back Mattie Pollock from Grimsby Town on a five-year contract for an initial fee of £250,000.
Pollock made his senior debut for League Two Grimsby aged 17 and his deal at Blundell Park had a year remaining.
Watford, managed by Xisco Munoz, have already signed England Under-18 forward Kwadwo Baah from Rochdale this summer.
Find all the latest football transfers on our dedicated page.