AceShowbiz - Arnold Schwarzenegger's former Mr. Universe training partner and best pal Franco Columbu has died.

The 78-year-old bodybuilder and World's Strongest Man competitor passed away during an incident at sea in his native Sardinia.

Franco also worked with Arnold on "The Terminator" and served as a stunt co-ordinator on his friend's film "Conan the Barbarian".

Upon learning of Columbu's death on Friday, August 30, Schwarzenegger posted a lengthy tribute on social media beneath a shot of the two best friends together, writing: "You've heard me say that I don't like when people call me a self-made man. You've even heard me say that you're part of the reason I could never accept that label. But I wanted you to know why. From the minute we met in Munich, you were my partner in crime. We pushed each other, we competed with each other, and we laughed at every moment along the way.

"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."

Confessing he has been left "devastated" by his pal's death, Arnie adds, "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."

"I will always miss you. But I'll also know that a part of you lives on in me... and in the millions of people you inspired every day you lived... I love you Franco. I will always remember the joy you brought to my life, the advices (sic) you gave me, and the twinkle in your eye that never disappeared. You were my best friend."

And actor Joe Manganiello also tweeted a photo tribute, writing: "RIP Franco Columbu... You were a friend and an inspiration."