Hazelwood admitted she never expected to revisit the beloved couple.
"I wrote a sequel to The Love Hypothesis is not a sentence I thought I'd say a year or so ago, but now I weirdly can't imagine a world in which The Two-Body Problem doesn't exist," she wrote on Instagram.
She credited the upcoming film adaptation of The Love Hypothesis for inspiring her return to the characters.
"The TLH movie and its cast made me fall for Adam and Olive all over again. Revisiting them was an absolute pleasure."
Hazelwood also acknowledged that some readers may prefer to imagine the couple's story ending with the original novel, telling fans they were free to "overwrite it with whatever headcanon you prefer."
For those returning to Adam and Olive, she described the sequel as "a mix of slice of life, postdoctoral turmoil, and unflinching exploration of the hardest challenge one will face in a long-term relationship: deciding what to have for dinner."
The announcement comes as anticipation continues to build for the film adaptation of The Love Hypothesis, starring Lili Reinhart and Tom Bateman.
Hazelwood also revealed that MRC is developing a film adaptation of The Two-Body Problem for Amazon MGM Studios, although she noted that the project has yet to be officially greenlit.