When was the first exoplanet found in the habitable zone of its star?

In 2011, NASA’s Kepler mission announced Kepler-22b, the first known planet in the habitable zone of a Sun-like star. The habitable zone is the range where temperatures could allow liquid water on a planet’s surface, depending on atmosphere and other conditions. Kepler-22b is much larger than Earth, so it is not necessarily Earth-like. Still, the discovery was an important milestone in the search for potentially habitable worlds.