What was the name of sequel made four years after original Frankenstein?

The sequel to the original "Frankenstein" novel, written by Mary Shelley, was titled "Frankenstein, or The Modern Prometheus".

However, it's important to note that "Frankenstein" is not a sequel to another book. It was published in 1818 and was the original story of the creation of the monster by Victor Frankenstein.

The sequel, which was published in 1823, wasn't a continuation of the first novel but rather a retelling of the story with a focus on the monster's perspective.