Harrison Wagner's Brother and Girlfriend Mourn the 27-Year-Old's Sudden Death: 'Always with You'

Harrison Wagner's brother and longtime girlfriend have paid tribute to the 27-year-old following his death Monday.

Harrison, the son of soap stars Jack and Kristina Wagner, was found dead in Los Angeles, according to a report from the Los Angeles Medical Examiner's Office obtained by PEOPLE. His cause of death has yet to be determined.

Sharing throwback photos of him and Harrison during their childhood years, brother Peter Wagner, wrote a short and sentimental message to remember Harrison.

"Always with you."

RELATED: Cause of Death for Jack and Kristina Wagner's Son Harrison Requires 'More Investigation': Medical Examiner

Harrison's on-and-off longtime girlfriend Sophia Bui also opened up about the loss in a heartfelt post that included a photo of her resting her head on Harrison's shoulder as he sweetly wrapped his arm around her.

Harrison, Peter, Jack and Kristina Wagner
Harrison, Peter, Jack and Kristina Wagner

Harrison Wagner Peter, Harrison, Jack and Kristina Wagner

In a "love letter to babe," Bui wrote, "I'm so broken hearted."

She said that they were supposed to see each other Friday and Harrison "called and apologized."

Harrison Wagner and girlfriend Sophia Bui
Harrison Wagner and girlfriend Sophia Bui

Harrison/instagram Harrison Wagner and girlfriend Sophia Bui

"Seven years, on and off, round and round we loved each other. For better or for worse. In sickness and in health. Sorry, I missed yr calls in the middle of the night these last few days," Bui continued. "I miss sleeping in yr pola bear arms, curled up. I miss sending you silly animal videos. I miss you sending gorgeous songs that made me cry."

She said that with Harrison, "I was never alone in this world with you. You were the balm that soothed my soul. You were my guy. I hope I was that comfort for you. I will always be yr babe. I will always choose to love you in this world and in any other life." Bui ended with several broken heart Emojis.

A spokesperson for the L.A. Coroner's Office told PEOPLE that Harrison's cause of death was still under investigation on Wednesday.

"Cause of death is deferred," the spokesperson said. "Deferred means that after an autopsy, a cause of death has not been determined and the medical examiner is requesting more investigation into the death, including additional studies."

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"Once the tests/studies come back, the doctor evaluates the case again and makes the cause of death determination," they continued.

Harrison is Jack and Kristina's youngest son. The former couple and one-time General Hospital costars, who were married from 1993 to 2006, also share Peter, 31. (When Calls the Heart star Jack, 62, also has a daughter, Kerry, from a previous relationship.)

Shortly before Harrison's passing, he wrote on Instagram: "Focus. YOU are left with YOU and your thoughts."