Prashant Kishor had been the vice president of Janata Dal United since 2018

Highlights Nitish Kumar expelled two of his aides - Prashant Kishor, Pavan Varma

The expulsions came after weeks of acrimony

In their parting shot on Twitter, both said "thank you"

Nitish Kumar, the Chief Minister of Bihar, on Wednesday expelled two of his closest aides, Prashant Kishor and Pavan Varma, after weeks of acrimony over their open criticism of his stand on the citizenship law. In their parting shot on Twitter, both said "thank you" and wished their ex-boss luck in retaining the "chief minister's chair".

The move was imminent. Nitish Kumar had declared over the past few days that the two were "free to leave".

Prashant Kishor, the ace election strategist credited with Nitish Kumar's 2015 Bihar victory, exits on the verge of another election.

"Thank you Nitish Kumar. My best wishes to you to retain the chair of Chief Minister of Bihar. God bless you," Mr Kishor tweeted.

Pavan Varma, who had rattled Nitish Kumar with an open letter referring to conversations criticizing the BJP, added: "Thank you Nitish Kumar ji for freeing me from my increasingly untenable position of defending you and your policies. I wish you well in your ambition of being CM of Bihar at any cost."

As vice president of Janata Dal United (JDU) since 2018, Mr Kishor had been virtual number two to Nitish Kumar. That relationship rapidly soured after Mr Kishor publicly called out his party boss in tweets and urged him to take a firm stand on the Citizenship (Amendment) Act CAA and the National Register for Citizens (NRC).

Mr Kishor questioned the party's support to the CAA in parliament just days after Nitish Kumar expressed his reservations at a party meeting. In December, he was persuaded by the JDU chief to drop the idea of quitting, but the social media attacks resumed.

Nitish Kumar betrayed his fury at Mr Kishor yesterday when he repeated a controversial comment on inducting Mr Kishor at BJP leader Amit Shah's instance.

"Someone wrote a letter I replied to it. Someone is tweeting, let him a tweet. What do I've to do with it? One can stay at the party till he wants. He can go if he wants...Do you know how did he join the party? Amit Shah asked me to induct him," he said.

Mr Kishor's response was quick and brutal.

"What a fall for you to lie about how and why you made me join JDU!! Poor attempt on your part to try and make my colour same as yours! And if you are telling the truth who would believe that you still have courage not to listen to someone recommended by Amit Shah," he tweeted.

Sources close to Mr Kishor said the comment was in poor taste just two days after Nitish Kumar took offence to Pavan Varma's letter referencing private conversations.

The startling claim on Amit Shah's recommendation had first surfaced in 2018 in Nitish Kumar's interview to a private channel.

Even Amit Shah had reportedly said it was "not right" to make such comments as these were private conversations.

This morning, a party leader, Ajay Alok, dragged the fight to a new low by comparing Mr Kishor to the deadly Coronavirus. "This man is not trustworthy. He could not win the trust of (Prime Minister Narendra Modi ji and Nitish ji. He works for AAP, talks to Rahul Gandhi, sits with Mamata didi (Mamata Banerjee). We are happy this #coronavirus is leaving us, he can go wherever he wants to," the former party spokesperson said.

Nitish Kumar's move not just underscores which side of the citizenship debate he is on, but also serves to reassure ally BJP as they prepare to contest the Bihar election later this year.