How hydronium ion is formed?

when a protic acid is added to water, it releases a hydrogen ion (H+) (also called aproton because a hydrogen atom missing one electron is nothing but a proton!). However, H+ will not stay a free ion, and instead immediately combines with a nearby water molecule (H2O) to form the hydronium ion, H3O+.

For example, when hydrochloric acid (HCl) is added to water, the following reaction occurs:

HCl + H2O --> H+ + Cl- + H2O --> H3O+ + Cl-