Huldbrand had suspected that he had seen the man before, and now felt assured that he was Kühleborn. Undine admitted the fact, and said that her uncle had told her a secret, which she was to reveal on the third day afterwards, which would be the anniversary of Bertalda's nameday.
The anniversary came, and strange incidents happened. After the banquet given by the duke and duchess, Undine suddenly gave a signal, and from among the retainers at the door came forth the old fisherman and his wife, and Undine declared that in these Bertalda saw her real parents. The proud maiden instantly flew into a violent rage, weeping passionately, and utterly refused to acknowledge the old couple as her father and mother. She declared that Undine was an enchantress and a witch, sustaining intercourse with evil spirits.
Undine, with great dignity, indignantly denied the accusation, while Bertalda's violent conduct created a feeling of disgust in the minds of all in the assembly. The matter was settled in a simple manner, for the duke commanded Bertalda to withdraw to a private apartment with the duchess and the two old folks from the hut, that an investigation might be made. It was soon over, for the noble lady was able presently to inform the company that Undine's story was absolutely true. The guests silently departed, and Undine sank sobbing into her husband's arms.
Next day Bertalda, humbled by these events, sought pardon of Undine for her evil behaviour, and was instantly welcomed with loving assurances of forgiveness, moreover, she was cordially invited to go with the pair to Ringstetten.
"We will share all things there as sisters," said Undine.
The three journeyed to the distant castle, and took up their abode together. Soon Kühleborn appeared on the scene, but Undine at once repulsed him. Next, when her husband was one day hunting, she ordered the great well in the courtyard to be covered with a big stone, on which she cut some curious characters.
Bertalda waywardly complained that this proceeding deprived her of water that was good for her complexion, but Undine privately explained to Huldbrand that she had caused the servants to seal up this spring because only by that way of access could her uncle Kühleborn come to disturb their peace.
As time passed on, Huldbrand gradually cooled toward his wife and turned affectionately towards Bertalda. Undine bore patiently and silently the sorrow thus inflicted on her. But when her husband was impatient and angry she would plead with him never to speak to her in accents of unkindness when they happened to be on the water, for the water spirits had her completely in their power on their element, and would seek to protect her, and even seize her and take her down for ever to dwell in the crystal castles of the deep.
After some estrangements, Undine and Bertalda had again become loving friends, and Huldbrand's affection for his wife had revived with its old and welcome warmth, while the attachment between him and Bertalda seemed forgotten.
One day the three were enjoying a delightful excursion on the glorious Danube. Bertalda had taken off a beautiful coral necklace which Huldbrand had given her. She leaned over and drew the coral beads across the surface, enjoying the glitter thus caused, when suddenly a great hand from beneath seized the necklace and snatched it down. The maiden's scream of terror was answered by mocking laughter from the water.