Facebook CEO Mark Zuckerberg will testify Tuesday that he's 'sorry' and that his firm 'didn't do enough' to protect the sites' users from having their personal information compromised.

The 33-year-old exec will make the apology when he testifies in blockbuster hearings  on Capitol Hill on Tuesday and Wednesday about how millions of users had their data harvested by filling out surveys that got to Cambridge Analytica.

Zuckerberg will defend Facebook as an 'idealistic and optimistic' company, before accepting personal responsibility for not setting up the right security protocols.

On Monday he toured senators' offices surrounded by Capitol Hill officers, with his disclosed meetings including Democrats Dianne Feinstein and Bill Nelson.

'It was my mistake, and I'm sorry,' he said, in House testimony released a day before his first grilling. 

Closely-guarded: Mark Zuckerberg was surrounded by Capitol Hill cops as he toured senators' offices Monday before blockbuster testimony which will start on Tuesday

Entourage: The Facebook CEO was accompanied by advisers and escorted by Capitol Hill officers as he met senators including Dianne Feinstein

Zuckerberg said he was 'sorry' he didn't do enough to protect Facebook users' privacy

Visit: Mark Zuckerberg leaves his Bill Nelson, Democratic senator from Florida

Facebook presence: Andrea Besmehn

'But it's clear now that we didn't do enough to prevent these tools from being used for harm as well,' according to Zuckerberg's prepared testimony.

'That goes for fake news, foreign interference in elections, and hate speech, as well as developers and data privacy.'

He continued: 'We didn't take a broad enough view of our responsibility, and that was a big mistake. It was my mistake, and I'm sorry. I started Facebook, I run it, and I'm responsible for what happens here.

'So now we have to go through every part of our relationship with people and make sure we’re taking a broad enough view of our responsibility,' he pledged.

After mentioning the estimated 126 million people who got content linked to the infamous Russian troll farm Internet Research Ageny, Zuckerber wrote: 'There's no question that we should have spotted Russian interference earlier.'

Zuckerberg is trying to earn some 'likes' from lawmakers, meeting privately Monday with some of those who will question him on the firm's privacy scandal later this week.

Facebook Founder and CEO Mark Zuckerberg met with lawmakers privately on Monday in advance of public hearings Tuesday and Wednesday, where he is expected to get a pounding from lawmakers angry about privacy issues

SO SORRY: Zuckerberg apologized in testimony released by the House Energy and Commerce Committee

The secret Monday meetings come in advance of Zuckerberg's Tuesday testimony before the House Energy and Commerce Committee and Wednesday before a joint hearing with the Senate Judiciary and Commerce panels.

The closed-door meetings run through Monday afternoon and include some of the members who will question Zuckerberg, Reuters reported.

The world's fifth richest man is being coached by a team of experts and a former George W. Bush aide about how to handle lawmakers waiting for the chance to interrupt him or bash Facebook's security practices.

He has retained a team from the top law firm WilmerHale as well as outside consultants. It even set up mock-hearings with consultants playing members of Congress, the New York Times reported.

OPEN DOOR: Facebook CEO Mark Zuckerberg arrives on Capitol Hill in Washington, Monday, April 9, 2018, to meet with Sen. Bill Nelson, D-Fla., the ranking member of the Senate Commerce Committee

Facebook CEO Mark Zuckerberg (3rd L) arrives at a meeting with U.S. Sen. Bill Nelson (D-FL), ranking member of the Senate Committee on Commerce, Science, and Transportation, as a member of the media tries to approach him April 9, 2018 on Capitol Hill in Washington, DC

PUT ME IN COACH: Zuckerberg has been getting coaching from Reginald Brown, who served as a special assistant and associate White House counsel to President George W. Bush

The behind-the-scenes prepping comes as Zuckerberg negotiated a media tour in which he accepted responsibility and the firm put out the bad and then worse news of how many millions of people had their data compromised.

'Their goal is to make Mr. Zuckerberg appear as humble, agreeable and as forthright as possible,' the Times reported, in a report sourced to people close to the operation.

One member of the team is Reginald Brown, who served as a special assistant and associate White House counsel to President George W. Bush.

Zuckerberg told reporters in a conference call he accepted blame for the policy that allowed political consulting firm Cambridge Analytica to acquire personal data on up to 87 million users.

Facebook has suspended another firm, CubeYou, after CNBC reported it engaged in a similar practice, relying on user surveys purportedly for academic research that then yielded information that ended up getting sold for commercial uses.

The company sold the data collected by researches for the Psychometrics Lab at Cambridge University.

'These are serious claims and we have suspended CubeYou from Facebook while we investigate them,' said a Facebook spokesman.

'If they refuse or fail our audit, their apps will be banned from Facebook.'

Facebook has been rolling out a PR strategy to deal with the scandal, but Zuckerberg is expected to face tough questioning in the televised hearings.

 "A day of reckoning is coming for websites like @facebook," tweeted Massachusetts Democratic Senator Ed Markey on Friday. "We need a privacy bill of rights that all Americans can rely upon,' he wrote.

Zuckerberg's private sit-downs with lawmakers come after a decade where the firm ramped up its Washington presence – and political contributions.

Facebook has given $7 million in campaign contributions to lawmakers since 2007, according to the Center for Responsive Politics.

That includes $985,000 to members of the three committees that will interrogate Zuckerberg Tuesday and Wednesday.

A Facebook spokesman said on Sunday that the company plans to begin telling the estimated 87 million users affected by the breach associated with Cambridge Analytica on Monday.

A massive breach of Facebook data could have 'absolutely' affected more than 87 million users, former research director of Cambridge Analytical Christopher Wiley said on Sunday.

'I think that it could be higher, absolutely,' the computer expert turned whistle blower said during an interview with NBC's 'Meet the Press' Sunday.

Wylie revealed last month that Cambridge Analytical had improperly collected the data of millions of Facebook users without their consent

Wylie revealed last month that Cambridge Analytical had improperly collected the data of millions of Facebook users without their consent

File - This Jan. 17, 2017, file photo shows a Facebook logo being displayed in a start-up companies gathering at Paris' Station F, in Paris.  Facebook is on the offensive to try to contain swirling concerns about how it protects the data of its 2.2 billion members. As CEO Mark Zuckerberg prepares to face Congress on Tuesday, April 10, 2018,  and the company rolls out new privacy rules, the social media juggernaut is facing the most serious challenge in its 14-year-history and seeking to maintain people's trust and avoid a user exodus.(AP Photo/Thibault Camus, File)

London-based Cambridge Analytica, which has counted U.S. President Donald Trump's 2016 campaign among its clients, has disputed Facebook's estimate of the number of affected users.

Zuckerberg is expected in his testimony to recognize a need to take responsibility and acknowledge an initial failure to understand how many people were affected, a person briefed on the matter, who asked for anonymity, said on Sunday.

Zuckerberg said in a conference call with reporters last week that he accepted blame for the data leak, which has angered users, advertisers and lawmakers, while also saying he was still the right person to head the company he founded.

On Friday, Facebook backed proposed legislation requiring social media sites to disclose the identities of buyers of online political campaign ads and introduced a new verification process for people buying 'issue' ads.

The steps are designed to deter the kind of election meddling and online information warfare that U.S. authorities have accused Russia of pursuing, Zuckerberg said on Friday. Moscow has denied the allegations.

In February, U.S. Special Counsel Robert Mueller charged 13 Russians and three Russian companies with interfering in the 2016 U.S. presidential election by sowing discord on social media.

Zuckerberg, on the call with reporters, said Facebook should have done more to audit and oversee third-party app developers like the one hired by Cambridge Analytica in 2014.