The devastated girlfriend of Australian surfer Callum Robinson revealed a heartbreaking voice message he had left her before he and two pals were killed while on a trip to Mexico last month.

San Diego local Emily Horwath posted the touching message from the 33-year-old Perth native, who was found slain at the bottom of a 50-foot well in Baja Mexico alongside his brother, Jake Robinson, 30, and their American friend, Jack Carter Rhoad, 30.

“Happy Tuesday! Good morning,” Callum said in the message she posted to her Instagram story, Australia’s 7 News reported.

“It’s 11:11 and I’m just thinking about you. Just wanted to drop you a quick message and say hello, baby.

“Hope you’re having a phenomenal start to your day. I’m sensing a big grin on your face for some reason today. I hope you’re full of positivity and smiles.

“Cheers, baby. Miss ya.”

Horwath wrote that she “Will be playing this on repeat” in the caption.

“This man changed my life in a way that I can’t even put into words,” she wrote in another post with a photo of her arms around Callum. “I don’t yet understand a world without him and his energy in it. I feel so grateful to have loved him.

“Tell your people you love them,” she continued. “Live life to the fullest every day be kind to others, laugh uncontrollably. Don’t let the small stuff bother you. lead with positivity. and live like Cal.”

The three friends were last seen alive on April 27 in the city of Ensenada.

Mexican authorities initially said that the three were victims of a violent carjacking — however The Post has learned that they may have been killed by cartel members looking for a rival gang, as Baja California is in the midst of a drug war.

Three people — Jesús Gerardo Garcia Cota, his partner Ari Gisel García Cota, and brother Cristian Alejandro Garcia — were arrested in connection to the three surfers’ disappearance, but at this stage haven’t been charged with murder.

Prosecutors allege the trio targeted the surfers for their cars’ tires before a confrontation turned violent. They then hid their bodies in a well about four miles away.

But that story doesn’t appear to add up, one source who does private security work in Mexico told The Post. Instead, he believes the surfers were misidentified as a rival criminal organization and murdered by the cartel.

“Given the deep and widespread corruption in the Mexican police, it’s hard to dismiss the possibility of a cover-up, potentially to shift blame away from a powerful drug cartel. This would certainly align with the Mexican government’s efforts to downplay the severity of cartel violence in Mexico,” the source said.

Prosecutors said a fourth body was also found at the bottom of the well. It is believed to be the remains of a rancher who owned the property and vanished two weeks earlier.