Riya and Veer

Is Riya Veer's half sister? I always thought she was his step sister because they were in the same class in SDCH and therefore the same age. I mean it's not impossible for a man to have children at the same time from two different women but I thought Anand got with Gayatri after Savitri went into coma. According to Wikipedia, Riya IS Veer's half sister...

She is gaytri daughter dear not mr anand malhotra