Katherine Schwarzenegger is heartbroken over the loss of her beloved horse, Cinco … sharing a flood of pics on IG, honoring their 20+ years together.

In her Tuesday post, Katherine wrote a heartfelt caption … saying goodbye to a pet is never easy, especially one who’d been part of every chapter of her life — even sizing up Chris Pratt on the now-married couple’s very first date.

Katherine shared Cinco had been with her since she was 11 … she’d do homework in the stalls — her safe haven — and lean on him through heartbreaks, first loves, worries, and every major life moment in between.

She revealed the barn was where she felt the most real and authentic version of herself … which makes losing Cinco all the more crushing.

Katherine’s post was seriously moving … proving her bond with Cinco was the real deal.