The eighth son was the Supreme Personality of Godhead Himself - Krsna. The highly fortunate Subhadra, the one daughter, was your (King Pariksit's) grandmother

Expressions researched:
"Krsna. The highly fortunate Subhadra, the one daughter, was your grandmother" |"The eighth son was the Supreme Personality of Godhead Himself"

SB Canto 9

The eight sons born of Sahadevā such as Pravara and Śruta, were exact incarnations of the eight Vasus in the heavenly planets. Vasudeva also begot eight highly qualified sons through the womb of Devakī. These included Kīrtimān, Suṣeṇa, Bhadrasena, Ṛju, Sammardana, Bhadra and Saṅkarṣaṇa, the controller and serpent incarnation. The eighth son was the Supreme Personality of Godhead Himself—Kṛṣṇa. The highly fortunate Subhadrā, the one daughter, was your grandmother.

SB 9.24.53-55, Translation and Purport:

The eight sons born of Sahadevā such as Pravara and Śruta, were exact incarnations of the eight Vasus in the heavenly planets. Vasudeva also begot eight highly qualified sons through the womb of Devakī. These included Kīrtimān, Suṣeṇa, Bhadrasena, Ṛju, Sammardana, Bhadra and Saṅkarṣaṇa, the controller and serpent incarnation. The eighth son was the Supreme Personality of Godhead Himself—Kṛṣṇa. The highly fortunate Subhadrā, the one daughter, was your grandmother.

The fifty-fifth verse says, svayam eva hariḥ kila, indicating that Kṛṣṇa, the eighth son of Devakī, is the Supreme Personality of Godhead. Kṛṣṇa is not an incarnation. Although there is no difference between the Supreme Personality of Godhead Hari and His incarnation, Kṛṣṇa is the original Supreme Person, the complete Godhead. Incarnations exhibit only a certain percentage of the potencies of Godhead; the complete Godhead is Kṛṣṇa Himself, who appeared as the eighth son of Devakī.