Donald Trump Jr’s account on X posted that his father had died, in a series of messages placed by a hacker on Wednesday.
In a string of now deleted posts, the account claimed his father had died and directed a racial slur at President Joe Biden.
The posts were on the page, which has 10 million followers, for less than an hour before being deleted.
The Trump Organization said that the account was hacked.
One of the posts read: “I’m sad to announce, my father Donald Trump has passed away. I will be running for president in 2024.”
Another said North Korea was “about to get smoked”, while one post wrote of “some interesting messages” with convicted sex offender Jeffrey Epstein.
Others mentioned Richard Heart, a cryptocurrency influencer facing fraud charges by the Securities and Exchange Commission, and YouTuber Logan Paul.
The posts began appearing after 08:00 ET (12:00 GMT).
His father posted an unrelated message on his Truth Social account while his son’s account claimed his demise.
“Don’s account has been hacked,” Andrew Surabian, a spokesman for Mr Trump Jr, posted on X, adding that the post was “obviously not true”.
Mr Trump Jr has since posted on X, formerly Twitter, but has not alluded to his account being compromised other than to “like” a tweet saying he had been hacked.
X has been contacted for comment. An automatic reply from the company’s press email reads: “Busy now, please check back later.”
Mr Trump Jr has continued to use the Elon Musk-owned platform.
Truth Social was founded by the former president after his X account was suspended in 2021 due to the risk of incitement of violence. It was later reinstated last November.
Mr Musk took control of Twitter in October 2022 in a $44bn (£37bn) deal and renamed it X.