Arnold Schwarzenegger is in mourning for his longtime and childhood pal, actor and champion bodybuilder Franco Columbu, who drowned while swimming off the eastern coast of Sardinia, according to Italian press accounts.

Columbu, 78, a native Sardinian, died while being rushed by helicopter to a hospital, La Nuova newspaper reported.

He was a former Mr. Olympia and Mr. Universe who lived in Los Angeles and appeared in the Schwarzenegger films “The Terminator” and “Conan the Barbarian.”

“I love you Franco,” Schwarzenegger tweeted, calling Columbu his best friend. “I will always remember the joy you brought to my life, the advices you gave me, and the twinkle in your eye that never disappeared.”

The tweet linked to an essay Schwarzenegger wrote detailing their long friendship.

“From the minute we met in Munich, you were my partner in crime,” he reminisced.

“We pushed each other, we competed with each other, and we laughed at every moment along the way,” the essay continued.

“When I finally got to America, I was alone. I’d left my family, my country, my whole life behind. So when I asked Joe Weider to bring you to train with me, it was because I knew I wasn’t the same without my best friend. I could thrive without money, without my parents, but I couldn’t thrive without you.

“I am devastated today. But I am also so, so grateful for the 54 years of friendship and joy we shared. The pumps, the chess games, the construction work, the meals, the pranks, the life lessons — we did it all together. We grew and we learned and we loved. My life was more fun, more colorful, and more complete because of you.”