President Donald Trump denounced outgoing British prime minister Theresa May, who only last month praised the “strong and enduring” ties between the UK and U.S., for making a mess of Brexit.

In his tweet slamming May, Trump also implied that if May had listened to his advice -- which he didn’t share -- she wouldn’t be mired in the Brexit mess that led to her resignation.

“I have been very critical about the way the U.K. and Prime Minister Theresa May handled Brexit. What a mess she and her representatives have created. I told her how it should be done, but she decided to go another way,” Trump tweeted Monday.

​The president then lashed out at British ambassador to the U.S., Sir Nigel Kim Darroch, who heaped scorn on Trump in a series of secret reports somehow leaked to British media on July 6.

“I do not know the Ambassador, but he is not liked or well​ ​thought of within the U.S. We will no longer deal with him​,” said Trump of Darroch.

May, however, said she has "full faith" in Darroch but didn’t agree with him. Her spokesman described the unprecedented leak of secret diplomatic material as "absolutely unacceptable." This declaration of support apparently led to Trump’s criticism of May’s handling of Brexit.

Trump’s comments came just days after the Darroch created a firestorm over leaked secret reports to the British government denouncing Trump as “inept,” “insecure” and “incompetent.” Darroch saw Trump as “radiating insecurity” and as a person who fills his speeches with “false claims and invented statistics.”

Darroch also noted Trump has “achieved nothing” in terms of domestic policy. He pointed out Trump’s economic policies might wreck the world trade system.

He also described the Trump administration and Trump himself as “dysfunctional.” He also said the bitter conflicts in Trump's White House cited by American media and verified by his own sources are “knife fights.”

More worrying to the British is Darroch’s belief that allegations of collusion between Trump and Russia remain in the realm of fact.

“The worst cannot be ruled out,” according to Darroch.

Sir Kim Darroch Ambassador Kim Darroch speaks to guests during the Capitol File 2017 WHCD Welcome Reception at the British Ambassador's Residence on April 28, 2017 in Washington, DC. Photo: Riccardo Savi/Getty Images for Capitol File Magazine

Darroch believes Trump’s presidency is living on borrowed time and might “crash and burn.” The Trump administration could also “be at start of downward spiral.”

“We don't really believe this Administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept,” wrote Darroch.