SB 10.61.23

yady apy anusmaran vairaṁ
 rukmī kṛṣṇāvamānitaḥ
vyatarad bhāgineyāya
 sutāṁ kurvan svasuḥ priyam
yadi api — although; anusmaran — always remembering; vairam — his enmity; rukmī — Rukmī; kṛṣṇa — by Lord Kṛṣṇa; avamānitaḥ — insulted; vyatarat — granted; bhāgineyāya — to his sister’s son; sutām — his daughter; kurvan — doing; svasuḥ — of his sister; priyam — the pleasing.
Though Rukmī always remembered his enmity toward Lord Kṛṣṇa, who had insulted him, in order to please his sister he sanctioned his daughter’s marriage to his nephew.

The answer to King Parīkṣit’s question is given here. Ultimately Rukmī approved his daughter’s marriage to Pradyumna in order to please his sister, Rukmiṇī.