Erik Wolpaw, the writer behind Half-Life 2 and Portal has returned to Valve after leaving the company in 2017. He left Valve to work with Double Fine Productions on the sequel to the iconic platformer, Psychonauts. Other than the two previously mentioned titles, Erik also worked on the original Portal and Left 4 Dead.
Gabe Newell (the boss of Valve) has confirmed the news as well. Erik himself didn't confirm anything and we know nothing about his next project at Valve. But, let's hope it's something epic again.