Kumar did not take any names, but it was clear that the leader in question was none other than Narendra Modi, the BJP's campaign committee chief for the 2014 polls, who went on to become the prime minister.
But then, there are no permanent friends and enemies in politics.
Here is a look at Kumar's previous statements, made after he quit the NDA alliance, which proves the adage:
2013 (after breaking 17-year-long alliance with the BJP): We cannot compromise with our basic principles. We are not worried about the consequences. But we had no alternative now. We are not responsible. We were forced to take this decision.
More From This Section
2015: He (Modi) raised question over my DNA. He called Lalu Prasad a 'shaitan' and me an 'ahankari'. Does speaking in such a language behove a person sitting on the responsible post of a PM?
2016: Sangh-mukt Bharat banane ke liye sabhi gair BJP parties ko ek hona hoga (to usher in a Sangh-free India all non-BJP parties have to come together).
"Whatever decision we have taken will be in the interest of Bihar and of its people. It will ensure development and justice. It will also ensure progress. This is a collective decision.
"I favoured opposition unity...But what kind of opposition unity was going to be there...There was no discourse, no agenda. Having a reactive agenda will not do," he said.