The famous Tycho supernova of 1572, witnessed by Danish astronomer Tycho Brahe, didn't explode in empty space as has been assumed. New analysis reveals it detonated inside a planetary nebula, the ghostly shell of gas expelled by an earlier dying star. The evidence lies in two "ear" shaped structures that were sticking out from the remnant's main shell, matching similar features in three other supernovae previously identified as explosions within planetary nebulae. This discovery supports the "core-degenerate" model where a white dwarf star merges with a companion star's core, with the explosion occurring hundreds of thousands of years later while the nebula remains intact. Most strikingly, if Tycho follows this pattern, it suggests that 70-90% of normal Type Ia supernovae may actually be supernovae inside planetary nebulae!