Doubtless she had been in another room and had slipped out while he was trying the door within.
He passed his hand over his eyes and breathed hard as he leaned against the wall, for her appearance there could only mean one thing, and that was ruin to her and disgrace to his name--the very end of all things in his life, in which all had been based upon his honour and every action had been a tribute to it.
He was too much stunned to ask himself how the lovers had met, if there had been any agreement between them, but the frightful conviction took hold of him that this was not the first time, that long ago, before Don John had led the army to Granada, Dolores had found her way to that same door and had spent long hours with her lover when no one knew.

Else she could not have gone to him without agreement, at an instant's notice, on the very night of his return.
Despair took possession of the unhappy man from that moment.

But that the King was with Don John, Mendoza would have gone back at that moment to kill his enemy and himself afterwards, if need be.

He remembered his errand then.

No doubt that was the very room where Dolores had been concealed, and she had escaped from it by some other way, of which her father did not know.