The decision on the timing of Priyanka's political plunge was taken some years ago. She was delaying it because of the children, he said, replying to a question at an interactive session here.
"Now her children are grown-ups. While one of them has entered university, another too has grown up. Therefore, she decided to join politics," he said.
On Priyanka's political role, Gandhi said her main job is to revive the Congress in Uttar Pradesh. No decision on her role outside that state has been taken.
Priyanka Gandhi Vadra plunged into active politics on Wednesday and was made AICC general secretary for Uttar Pradesh East in a move reflecting the party's intent to go full throttle in the northern state in the run-up to the parliamentary polls.
Stating that he and Priyanka share a strong bond, the Congress president said "both of us have been through hell together" as he recalled the assassinations of his grandmother Indira Gandhi, father Rajiv Gandhi and subsequent political upheavals in the family.
"These incidents have brought us closer. Everybody thinks all is easy for us but we have seen some very hard situations. That has brought us together," Gandhi said.
About the equation between them, he said, "If we are sitting in separate rooms and you ask us the same questions, 80 per cent of the time you will get the same answer."
The Congress president said both he and his sister believe in giving space to each other and there is a constant give and take and spirit of reciprocity between the two when it comes to their personal relations.
"We have a lot of conversation," he added.