It's a self-seeded Calibrachoa and looks like a cross between two varieties I have grown in the past.
However, Calibrachoa are supposed to be sterile. Therefore, I have a bit of a mystery on my hands. It definitely is a Calibrachoa. But how did it sprout up (without being newly planted) in a pot that wintered outside in -15-degree weather and several prolonged below zero stretches over Winter 2024/2025???