The stage of the cell cycle in which the cell's nucleus divides is called Mitosis.

Here's a breakdown:

* Cell Cycle: The entire life cycle of a cell, from its creation to its division.

* Mitosis: The process of nuclear division, where the replicated chromosomes are separated into two identical nuclei.

Mitosis is further divided into four stages:

1. Prophase: The chromosomes condense, the nuclear envelope breaks down, and spindle fibers form.

2. Metaphase: The chromosomes line up along the center of the cell (the metaphase plate).

3. Anaphase: The sister chromatids (identical copies of chromosomes) separate and move to opposite poles of the cell.

4. Telophase: The nuclear envelope reforms around each set of chromosomes, and the chromosomes uncoil.

Following mitosis, the cytoplasm also divides in a process called cytokinesis, resulting in two identical daughter cells.