Half-Life 2: Episode Three

Nothing concrete is known about the third installment of the Half-Life 2 Episodes series except that it does indeed exist and is in the early stages of development. Valve consider the Half-Life 2 Episodes series to be a trilogy at this point, though a fourth 'episode' was once said to be in development by another developer. These rumours have mostly been forgotten as developers have said many times that 'Half life 2 Episode 3 will mark the end of the Half life 2 trilogy, however not the end of the Half Life franchise'.