The defender who turned 20 on Wednesday has signed a new two-year contract with the option of an extra year.
It comes less two months after making his senior debut for the Millers
Douglas spent most of 2024-25 on a season-long loan with Conference North club Warrington Town, making 31 league appearances for them.
But shortly after taking over as caretaker manager, Hamshaw recalled Douglas, and used him from the bench against Bolton and Mansfield
That show of faith meant a lot to the defender, and has been backed up by a new deal now Hamshaw has become the full-time manager.
“He trusted me straight away," said Douglas a product of the Millers' academy.
“He recalled me, and put me in the squad at the first opportunity. He’s just been great with me.”