checked = "checked " stops working when I add ngModel in mat-checkbox

My mat-checkbox's checked = "checked" stops working when I add an ngModel to it.

This will work.

<mat-checkbox name="BlackBeard" ngModel checked = "checked"> Zehahaha? </mat-checkbox>

This will not work.

<mat-checkbox name="BlackBeard" ngModel checked = "checked"> Zehahaha? </mat-checkbox>