Tiernan Brooks joined Charlton in January 2026 from Gateshead for an undisclosed fee.
The Sheffield-born goalkeeper came through the academy at Notts County and gained valuable senior experience during a number of loan spells, before joining Gateshead in the summer of 2024.
A Republic of Ireland youth international, he has represented his country five times at U21s level.
Brooks has put pen to paper on a two-and-a-half year deal at Charlton, with a club option of a further year.