It's been a while since we've had a major White House departure. As we wrap up our live coverage, here's what's gone on today, in brief:

• John Bolton has left his role as the US National Security Adviser, the third person to take the job under Donald Trump. His number two, Charlie Kupperman, has taken over for now
• It's unclear if Mr Bolton quit, or was fired - President Trump said he "disagreed strongly" with him and asked him to leave, but Mr Bolton said he offered his resignation on Monday
• No reason has officially been given for Mr Bolton's departure, but there's speculation the pair clashed over the president's plan to invite the Taliban to his Camp David retreat
• Mr Bolton has a more aggressive, "hawkish" foreign policy approach than Mr Trump, who wants US troops out of Afghanistan quickly
• Secretary of State Mike Pompeo said the president "should have people he trusts and values" on his staff

You can follow any further developments on our main news story here. But for now, that's it from us in London.

Image source, Getty Images

Thick, white and bushy – Mr Bolton’s moustache is his signature look.

But according to former White House strategist Steve Bannon, Mr Trump was not a fan.

It was Mr Trump’s aversion to Mr Bolton’s facial hair that originally cost him a cabinet position, Mr Bannon told Fire and Fury author Michael Wolff.

"Bolton's moustache is a problem. Trump doesn't think he looks the part," Mr Bannon reportedly said.

Mr Bolton and Mr Trump did not always see eye-to-eye. Indeed, when announcing Mr Bolton’s departure, Mr Trump said he “disagreed strongly with many of his suggestions”.

Mr Bolton did have a hand in some of Mr Trump’s major security decisions.

Most notable was Mr Trump’s decision to withdraw the US from the 2015 Iran nuclear deal. But while Mr Trump favoured a new deal with Iran, Mr Bolton wanted to overthrow its regime altogether.

Image source, Reuters

Regime change in Venezuela and North Korea was on Mr Bolton’s agenda, too.

In Venezuela, Mr Bolton helped orchestrate a campaign to remove President Nicolás Maduro from power. In North Korea, Mr Bolton lobbied Mr Trump to end Kim Jong-un's reign with a pre-emptive strike.

Neither happened on his watch, and Mr Trump went his own way on North Korea, hosting media-friendly summits instead of raining down missiles.

Pacts and deals, it seems, are not words in Mr Bolton’s vocabulary. He also pushed for Mr Trump to pull out a key nuclear treaty with Russia this year.

Towards the latter stages of Mr Bolton’s time in office, it was the war in Afghanistan that widened his rift with Mr Trump.

To Mr Bolton's dismay, Mr Trump announced the withdrawal of thousands of US troops from Afghanistan. To make matters worse, Mr Bolton was sidelined from talks with the Taliban to end the 18-year conflict.

Mr Trump has finished his speech at the Historically Black Colleges and Universities, and did so without once mentioning Mr Bolton, and sticking to the autocue (almost) the whole time.

President Trump is currently speaking at an event for Historically Black Colleges and Universities.

He seems to be staying very much on script... for now.

The stand-in national security adviser is one Charlie Kupperman.

Mr Kupperman is a former defence contractor executive, holding senior positions at Lockheed Martin and Boeing.

In January Mr Kupperman, a former Reagan administration official, was hired as Mr Bolton’s deputy.

Mr Kupperman’s appointment was criticised by civil rights groups, which condemned his links to right-wing think tank the Center for Security Policy (CSP).

Under Reagan’s administration, Mr Kupperman served in a number of roles, including for the Executive Office of the President and NASA.

Speaker of the house Nancy Pelosi has posted her response to Mr Bolton's departure on Twitter, tapping into fears about national security and the US position on the global stage.

She is the most significant Democrat to have responded to the news so far.

In the next few minutes, President Trump is expected to speak in Washington DC at the National Historically Black Colleges and Universities Conference.

Surely he won't be able to avoid commenting on Mr Bolton's departure...?

Image source, Reuters

John Bolton has long had a reputation as a hawk - someone whose approach to foreign policy is more on the aggressive, pro-conflict side.

He openly criticised the president’s attempts at dialogue with North Korea, and favoured a more confrontational approach to Iran.

He's been a conservative since he was a teenager, taking time off school at the age of 15 to help Barry Goldwater's presidential campaign in 1964.

Mr Bolton went to Yale, as a contemporary of Bill and Hillary Clinton - although he says they ran in different circles. Despite his hawkish stance nowadays, he avoided the Vietnam War draft, serving instead in the National Guard.

He went on to work for Ronald Reagan and both George HW and George W Bush's administrations - notably helping to build the case that Iraq's leader Saddam Hussein had weapons of mass destruction. This was later proved to be false.

You can read more about him in our profile here.

Image source, Getty Images

In the White House press conference, Secretary of State Mike Pompeo has been dealing with reporters' quickfire questions with a big grin on his face.

Treasury Secretary Steve Mnuchin doesn't look like he's enjoying it as much.

Asked right now if Mr Trump's national security team was a mess, Mr Mnuchin replied:

Secretary of State Mike Pompeo delivered some pointed comments about life in the Trump White House. Have a watch here:

Jon Sopel
BBC North America Editor

Mr Bolton played a pivotal position in forming the policy of Mr Trump's administration.

Was his departure a surprise? Yes - no-one had seen it coming.

Mr Bolton seemed much more keen than Mr Trump to get involved in a fight with countries like Iran and Venezuela.

The conventional narrative is that Donald Trump is impetuous and trigger-happy and he needs adults to restrain him, like John Bolton. Actually I think the truth was the other way round.

This seems to have been a very bitter parting of ways.

It’s worth bearing in mind that, only days ago, Mr Trump announced that he had called off peace negotiations with the Taliban.

Mr Trump was due to meet Afghan President Ashraf Ghani and senior Taliban leaders at his Camp David retreat. The venue for the secret talks and the timing - a few days before the anniversary of 9/11 - provoked controversy.

Reports said that Mr Bolton had argued that inviting a designated terror group to the US would set a terrible precedent. Mr Trump, ever the deal-maker, seems to have disagreed.

Eager to secure a deal that would pave the way for the withdrawal of thousands of US troops from Afghanistan, Mr Trump embraced the meeting.

Then at the 11th hour, it was cancelled, after the Taliban admitted to an attack in Kabul.

Incidentally, a CNN reporter, citing two sources, said Mr Bolton and Mr Trump got into a “bitter argument last night” over the Taliban talks.

For Mr Bolton, it may have been the row that set the scene for his departure.

If you're former national security adviser John Bolton, you may want to look away now.

As we just mentioned, Secretary of State Mike Pompeo is in the middle of a press conference - the US has issued new sanctions against what it designates as terror groups.

But the only thing the press wants to know about is John Bolton's departure.

Here's what Mr Pompeo had to say:

Asked by a reporter if he and Mr Mnuchin were "blindsided" by the departure - Mr Bolton was supposed to have attended the briefing too, after all - Mr Pompeo responded, with a smile:

In a few minutes, there's going to be a press briefing from the White House.

Two people will be speaking - Secretary of State Mike Pompeo and Treasury Secretary Steve Mnuchin. A third man was due to appear - a certain John R Bolton - but he won't be there, for reasons we've already made clear.

We'll bring you any lines from the press conference if/when they appear.

Anthony Zurcher
BBC North America reporter

John Bolton was always an unusual fit in the Trump White House. While he was an animated personality on Fox News - clearly endearing him to the president - he was also an outspoken foreign policy hawk working for a man who campaigned against international adventurism.

Mr Bolton was a strong supporter of the Iraq War, for instance, while the president has called the conflict one of the greatest US military blunders.

On topics like North Korea and Russia, the president's conciliatory position when Mr Bolton arrived in April 2018 was clear - and clearly contrary to the long-time foreign policy hand. Add disagreements on Afghanistan negotiations and Iran confrontation, and it created an untenable situation.

Mr Trump's third national security adviser in as many years has been on the outs for some time. He did not join the president at meeting with Kim Jong-un, and phoned-in his objections to a Camp David event with the Taliban while in Poland last week.

There appears to be disagreement over whether Mr Bolton was fired or resigned. One way or another, a change was coming - even if just yesterday, Mr Trump had tweeted that reports of "turmoil in the White House" were created by the "Dishonest Media".

Tara McKelvey
BBC News, Washington

Hogan Gidley, a White House spokesman, tells me that the acting US national security adviser is now Charles Kupperman (he served as a deputy to John Bolton).

Mr Bolton is the third person to serve as Trump's National Security Adviser.

The first was Michael Flynn. News junkies may remember that he pleaded guilty to lying to the FBI about contacts with Russia. Charges were brought against him as part of Robert Mueller's investigation into alleged Russian meddling in the 2016 election.

You can read more about Flynn here.

Image source, Reuters

The second was Herbert Raymond McMaster (H.R. for short). The general reportedly rubbed the president up the wrong way - Mr Trump said his briefings were "gruff and condescending".

Read more about number two in our profile here

So who will be number four...?

We've got word from a former senior Trump administration official - who wants to stay anonymous - that Mr Bolton operated "separately from the rest of the White House".

This official says Mr Bolton didn't go to meetings, and was "running his own show".

You can read more about it in our main news story here

It’s Joshua Nevett here, joining Toby on the BBC World online desk in London.

Mr Bolton's departure from the White House is a big deal. He was considered to be the architect of some of Mr Trump’s biggest national security decisions.

He was always seen as a foreign policy "hawk" - eager for action, and to take a tough stance on Iran, Syria, Venezuela and North Korea, for example.

Ultimately, his job was to give the president advice on all matters of national security and foreign policy. Sometimes, Mr Bolton had it his own way: he played a big part in Mr Trump’s decision to withdraw the US from the Iran nuclear deal.

Other times, his advice was seemingly ignored. Especially on the thorny issue of North Korea, whose leader, Kim Jong-un, Mr Bolton has always maligned as a dictator who ought to be deposed.

Nevertheless, Mr Bolton has enjoyed influence in the White House, which can’t be said for all his predecessors.