The 43-year-old singer, who already has a son, Rocket, with Lasichanh, broke the news while stepping out from a dinner party, which was hosted to celebrate their new fragrance in Los Angeles, reported People magazine.
Lasichanh, 36, a model and designer, and Williams are together for years before tying the knot in October 2013.
Meanwhile, Williams also previously opened up about why he and Helen chose to name their son Rocket.
"In the same way the Indians named their children after a force or animal or element, we named him after a man-made machine that was meant to go up, meant to ascend," he said that time.