The Denise Richards and Aaron Phypers divorce just got uglier … because Aaron beelined it to a police station and filed a report over the blowout fight that led to their split … TMZ has learned.

Aaron was spotted by paparazzi going into a Los Angeles County Sheriff’s Department station in Calabasas over the weekend … he wasn’t in the mood to talk to a photog, but now we know why he was there.

Law enforcement sources tell TMZ … Aaron came into the lobby of the Lost Hills station Sunday and spoke to a deputy about an alleged incident and a police report was taken.

In an exclusive interview, Aaron previously told us he caught Denise cheating on him and found messages between her and another man on her laptop, and saved them on his phone.

Aaron claims on July 4 he found his phone smashed into pieces in a recycling bin … and he alleges Denise smashed the device because it contained photos of texts proving she carried on the alleged affair.

For her part, Denise has claimed the July 4 fight started with Aaron verbally abusing her and demanding his phone. Aaron said his phone was missing for more than a day and when he questioned Denise about it she hit and scratched him.

Aaron filed for divorce July 7 and listed July 4 as the date of separation. Denise has since filed for and been granted a temporary restraining order against Aaron, alleging domestic abuse. Phypers has denied all claims of physical and emotional abuse against him.