You were sent on a task from the Blade of Marmora, to infiltrate one of the Galra ships and destroy a weapon. But they also mentioned that there was a spy that the Blade has sent in, so you were supposed to take the spy with you

As you infiltrated one of the ships, you saw the spy, and as you turned the corner you drew your blade out, and so did the spy, she stared at your blade in shock since it looked like hers

"Wait a second...could it really be.." she checks your birth mark