R being born was never shown, nor was he shown when Tunveer later came back in QH1 to marry Mr. Siddiqui and two years later (after the twins were born) kill Mr. K and Zoya and set SM ablaze. In QH2 it was revealed that R was left at an orphanage up until he was 5 years old or so, and when ARI's father saw Tunveer, fell for her beauty and married her, she took R from the orphanage and introduced him to everyone as a charity case that they would keep in the house.
We are never shown when he exactly came to know she is his mom since in the will-of-ARI's father scene (the night S is interred in the cemetery and ARI rescues her) he already knew her as his mother.Even so, his nature is mild and unassuming and he is grateful for the rich house for taking him in, educating him, and treating him much as a part of the house.His father - Imraan - also H's father, makes H and him half-siblings (not step-siblings).Somewhere it was mentioned that Imraan went to the middle-east and died there two years later.Jayne