The tribute, posted on Instagram to Lohan's 8.1 million followers, included a black-and-white snapshot of the pair smiling for the cameras as they held hands attending the 63rd International Venice Film Festival in September 2006, ET online reported.
"Best friends. Best life," Lohan emotionally captioned the tribute.
The body of Morton, 38, founder of the Pink Taco restaurant chain, was found in his Beverly Hills home by his younger brother Matthew. The death was confirmed by a spokesperson for the Beverly Hills Police Department, ET online reported.
The spokesman told the website there was no evidence of foul play and an autopsy was pending.
WOMAN'S EDITS OF INSTAGRAM PHOTOS WITH EX-BOYFRIENDS GO VIRAL: 'I CAN DO BETTER'
Morton was the son of business tycoon Peter Morton, co-founder of Hard Rock Cafe and Hotels, and the grandson of Arnie Morton, founder of Morton’s The Steakhouse, the report said.
CLICK HERE TO GET THE FOX NEWS APP
In addition to starting Pink Taco, with locations in Los Angeles, Chicago, Boston and Las Vegas, he once owned the Viper Room nightclub in West Hollywood and was an investor in Beacher’s Madhouse.
Morton was romantically linked to several other stars over the years — including Paris Hilton and Britney Spears, ET online reported.