The RJD chief's wife Rabri Devi will head the legislature party of the bicameral body.
Lalu, who had been authorised by the party MLAs earlier to take the decision, made the announcement today, his close aide and MLA Bhola Yadav told PTI.
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While Tejashwi Yadav is the Deputy Chief Minister of the state, Rabri Devi is a member of the state Legislative Council.
Tejashwi's appointment highlights the RJD chief's efforts to guide his younger son to become his heir apparent.
After the recent Assembly elections, RJD has 80 members in the 243-member Bihar Assembly.