Former FBI lawyer Lisa Page lied to bosses at the bureau about her affair with agent Peter Strzok — telling FBI Deputy Director Andrew McCabe that the pair were never romantically involved, a bombshell new book claims.

Page was “acutely embarrassed, mortified” when McCabe approached her in December 2016 to say he had heard rumors she was having an affair with Strzok, journalist James B. Stewart claims in his new book, “Deep State: Trump, the FBI, and the Rule of Law,” out Tuesday.

“‘I know you and Peter are friends, but you have to be more careful,'” McCabe, who became acting FBI director in the wake of James Comey’s dismissal, reportedly told Page.

“‘People are talking and this isn’t good for you,'” McCabe allegedly warned the senior lawyer, whom Stewart described as McCabe’s “confidant.”

“She denied the two were romantically involved or had had an affair,” Stewart wrote, claiming Page then went to the source of the rumor, head of counterintelligence Bill Priestap, to tell him the affair was not true.

The conversations among the trio were casual and not part of any official investigation — Priestap also telling Strzok, “We all have personal lives” and “I’m not the morality police,” Stewart wrote.

But the affair became public a year later in December 2017 when the Department of Justice released hundreds of text messages between the pair mocking Donald Trump and his supporters — calling the then-candidate a “disaster.”

The scandal became central to President Trump’s belief that there was bias in the FBI investigation into Russian interference in the 2016 presidential election that Strzok led and Page worked on.

Strzok was the lead investigator into Russian interference in the 2016 presidential election and Hillary Clinton’s use of her personal email server.

“No one was more steeped in the details of the Russian investigation than Strzok,” Stewart wrote.

Republican lawmakers and Trump said the nature of the disparaging messages shared by the lovebirds showed the FBI was biased against Trump.

“At the center of this supposedly dark conspiracy were Comey, McCabe, Page and Strzok,” Stewart wrote after the investigation showed Strzok was sending anti-Trump tweets while investigating Clinton.

In March 2016, Page told Strzok: “God Trump is a loathsome human.”

“OMG [Trump’s] an idiot,” replied Strzok.

“He’s awful,” Page told her lover, before he responded, “God Hillary should win.”

Page could not be immediately reached for comment.

According to Stewart, Comey and the FBI also had concerns about a potential pro-Clinton bias at the Justice Department in the midst of an investigation into her use of a private email server.

Comey was particularly “troubled” by then-Attorney General Loretta Lynch after he received a report from a “highly placed informant” that suggested Lynch was trying to shut down the investigation.

The document contained an email that Deborah Wasserman Schultz, chair of the Democratic National Committee, reportedly sent to an executive at Open Society Foundations, founded by billionaire Democratic donor George Soros.

“Wasserman Schultz assured [executive Leonard] Benardo that Lynch wouldn’t let the Clinton investigation get very far, suggesting that Lynch would protect Clinton,” Stewart wrote.