Donald Trump sits down with "Morning Joe" in Iowa in January. REUTERS/Scott Morgan Donald Trump took his escalating feud with "Morning Joe" to a new level on Monday, threatening to "tell the real story" of the relationship between hosts Joe Scarborough and Mika Brzezinski.

In a series of tweets on Monday, the Republican presidential nominee slammed the MSNBC hosts over their criticism of his brash campaign style.

Trump claimed that he would share information about the personal relationship between the two hosts — the subject of much speculation.

"Tried watching low-rated @Morning_Joe this morning, unwatchable! @morningmika is off the wall, a neurotic and not very bright mess!" Trump wrote.

Scarborough quickly responded in kind on Twitter, slamming the real-estate mogul over his comments about Brzezinski and refuting Trump's claims that the show's ratings are low.

Trump's comments on Monday come after months of criticism from the MSNBC hosts.

Last week, Scarborough authored an op-ed in The Washington Post urging Republicans to remove Trump from the ticket, citing his plan to bar all Muslims from entering the US and his refusal to tone down his occasionally authoritarian rhetoric.

The relationship between the hosts and Trump wasn't always tense.

Earlier in the campaign, critics charged the MSNBC hosts of going too easy on the real-estate magnate, who Scarborough and Brzezinski predicted would be successful in the Republican primary. Scarborough told an audience at a New York event last year that he'd given Trump some advice in preparation for the Republican presidential debates. And during an interview in February, Trump characterized the hosts as "supporters," though both hosts denied the assertion.