Samajwadi Party patriarch Mulayam Singh Yadav's daughter-in-law Aparna Yadav joined the Bharatiya Janata Party on Wednesday.
She joined the party in the presence of Uttar Pradesh Deputy Chief Minister Keshav Prasad Maurya and its state chief Swatantra Dev Singh.
She is married to Prateek Yadav, son of Mulayam Singh Yadav's second wife; Samajwadi Paaty president Akhilesh Yadav is his son from the first marriage.
Aparna Yadav said she has always been impressed with Prime Minister Narendra Modi, and added that the nation's interest has always been her priority.
There had been much speculation about her joining the BJP, and the development highlights the rift in the SP's ruling family at a time when Akhilesh Yadav has been working to rally the party's base in the run-up to the state assembly polls.
The BJP may field her in the polls, sources said.
Aparna Yadav had contested the 2017 assembly polls on the Samajwadi Party ticket from Lucknow Cantt but had lost to the BJP's Rita Bahuguna Joshi, now a Lok Sabha member.
Assembly polls in Uttar Pradesh will be held in seven phases beginning from February 10.