Once seen as the right-hand man of Yogi Adityanath, at least till he became the Uttar Pradesh Chief Minister three years ago, former chief of Hindu Yuva Vahini (HYV) Sunil Singh on Saturday joined the Samajwadi Party. Mr Singh was inducted into the SP in the presence of party chief Akhilesh Yadav and Samajwadi Party patriarch Mulayam Singh Yadav.