That's Floyd Mayweather reflecting on the birthday of his late, longtime-girlfriend and mother of his 3 children, Josie Harris, who would've turned 42 years old today.

Harris was tragically found dead at her Valencia, CA home back in March 2020.

Emergency responders received a call around 9:30 PM for a woman, Josie, who was found unresponsive in her car. Unfortunately, medics weren't able to save Harris ... and she was pronounced dead at the scene. Foul play was not involved.

Tragic news for the Mayweather family.

Floyd and Josie dated for around 15 years ... reportedly from about 1990 to 2005. They have 3 kids together ... Kouran, Zion, and Jirah Mayweather.

And, even though almost 2 years have passed, it's obvious Floyd -- not typically one to show emotion -- is still having a tough time dealing with the loss.

Mayweather went to Instagram and posted a photo of the mausoleum where Harris was laid to rest.

The stone is marked with a "Happy Birthday" decoration ... and a bouquet of flowers.