Here's why:

* Haploid: A haploid cell contains only one set of chromosomes (n).

* Zygote: A zygote is formed when a sperm cell (haploid) fertilizes an egg cell (haploid).

* Fusion: During fertilization, the haploid nuclei of the sperm and egg fuse together, resulting in a single cell with two sets of chromosomes (2n).

Therefore, a zygote initially contains two haploid nuclei before they fuse to form a diploid nucleus.