Franco Columbu smiles as he lifts weights in Los Angeles in 1978.
CNN  — 

Arnold Schwarzenegger is mourning the loss of the man he called his best friend – Italian bodybuilder Franco Columbu.

The 78-year-old Columbu was the best man at the wedding of Schwarzenegger and Maria Shriver in 1986. He was also an actor.

“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,” Schwarzenegger wrote in his tribute Friday. “I am devastated today. But I am also so, so grateful for the 54 years of friendship and joy we shared.”

Arnold Schwarzenegger stands next to Franco Columbu, hanging upside down, in this image from 1977.

Columbu died at an Italian hospital after “not feeling well” while swimming near his native town of Ollolai, on the Italian island of Sardinia, according to the Italian news service ANSA and the newspaper La Repubblica.

The mayor of the town, Efisio Arbau, told La Repubblica that Columbu’s death was “very painful” and that he was “Ollolai’s ambassador to the world.” Columbu lived in Los Angeles but returned to Sardinia for three weeks every August, Arbau told the newspaper.

Columbu was a world-class bodybuilder who was named Mr. Olympia twice, once in 1976 and again in 1981. He was also an actor who appeared in several of Schwarzenegger’s movies, including “Terminator.”

Columbu leaves behind his wife, Deborah, whom he married in 1986, and their daughter, Maria.