Joe Scarborough's brother, a longtime Trump supporter, called for the president to publicly apologize after he "crossed the line" by suggesting the former GOP lawmaker and television host be investigated over a congressional aide that was found dead in his office in 2001.

George Scarborough, businessman and MSNBC "Morning Joe" host's brother, endorsed Trump during his presidential campaign, and spoke during a 2016 rally for the then-GOP candidate, according to Floridapolitics.com.

"Outrageous reference re @JoeNBC where @potus @realdonaldtrump just crossed the line with me," the television host's brother tweeted Wednesday. "I need to see a public apology to my brother Joe or else he has lost my support for good ... which is saying a ton given all the support I’ve shown him in past 2 years."

Trump on Wednesday suggested Joe Scarborough be investigated in relation to the "unsolved mystery" surrounding the death of one of his congressional aides in 2001.

"So now that Matt Lauer is gone when will the Fake News practitioners at NBC be terminating the contract of Phil Griffin?" Trump tweeted. "And will they terminate low ratings Joe Scarborough based on the 'unsolved mystery' that took place in Florida years ago? Investigate!"

Trump appears to be referring to the death of Lori Klausutis, who was found dead in Scarborough’s district office in Okaloosa County, Fla., in July 2001.

The 28-year-old congressional aide had an abnormal heart rhythm and lost consciousness. She fell and hit her head on a desk, which ultimately led to her death, according to a medical examiner.

Scarborough denied any involvement in her death. In a letter to Variety Fair in 2005, the former lawmaker said he had only met the aide on three occasions and was never alone with her.

Scarborough addressed Trump's Wednesday tweets, saying the president was "not well."