She could learn it not only from Clara, but from himself.

He could not now be there at the house without showing that he both loved and knew that he was beloved.

And then why should Lady Desmond not know it?
Why should he think that she would set herself against the match?
He had certainly spoken to Clara of the difference in their rank; but, after all, it was no uncommon thing for an earl's daughter to marry a commoner.
And in this case the earl's daughter was portionless, and the lover desired no portion.

Owen Fitzgerald at any rate might boast that he was true and generous in his love.
So he plucked up his courage, and walked on with a smiling face to meet Lady Desmond and her son; while poor Clara crept beside him with eyes downcast, and in an agony of terror.
Lady Desmond had not left the house with any apprehension that there was aught amiss.

Her son had told her that Owen had gone off "to do the civil to Clara;" and as he did not come to the house within some twenty minutes after this, she had proposed that they would go and meet him.
"Did you tell him that I wanted him ?" said the countess.
"Oh, yes, I did; and he is coming, only he would go away to Clara." "Then I shall scold him for his want of gallantry," said Lady Desmond, laughing, as they walked out together from beneath the huge portal.
But as soon as she was near enough to see the manner of their gait, as they slowly came on towards her, her woman's tact told her that something was wrong;--and whispered to her also what might too probably be the nature of that something.