Hiding information to HR

I joined a new organisation on 1 july but i didn’t like the environment and didn’t see my growth so i started looking for job again.

So hr from one organisation contacted me and i told him i have 13 days of notice period left which is already over on 30 june, and i have an offer but didn’t tell him about my new employer.

Fast forward to now i received the offer from the organisation and have final round with senior HR, what should i do, should i tell them about my situation. Though i will join the organisation within week only

Will it lead to offer rejection.