The "Vanderpump Rules" alum and "The Valley" star beelined it to court Tuesday and filed divorce documents after 5 years of marriage ... according to new legal docs obtained by TMZ.

In the docs, Brittany is going with irreconcilable differences as the reason for the split. The estranged couple previously announced their separation in February, and Brittany lists the date of separation as January 24, 2024.

Brittany and Jax have one child together ... their 3-year-old son Cruz ... and Brittany's seeking primary legal and physical custody ... but is open to visitation for Jax.

Brittany also wants to block the ability of the court to award spousal support to either of them.

Brittany's divorce filing comes after Jax left a treatment center and returned to work on his new Bravo reality show "The Valley."

TMZ broke the story ... Jax decided he needed inpatient treatment for his mental health issues in the wake of his separation from Brittany.

Brittany and Jax started dating way back in 2015 ... they got engaged in June 2018 at Neptune's Net in Malibu, and in June 2019 they tied the knot at the Kentucky Castle in Versailles, KY.

They went through a lot together on 'VPR' before they had a number of marital challenges documented on season 1 of "The Valley" ... and now they're going through a divorce.