Franz Ferdinand and #WWIII: Why are these words trending?
Following the death of Iran's top military commander, there's a lot of speculation about what might happen next.
General Qasem Soleimani was killed by American drones in Iraq.
It's escalated an already-tense situation between Iran and the US.
Alongside his name, phrases like Franz Ferdinand and World War Three have been trending, with plenty of mentions for the man who ordered the strike - President Donald Trump.
So here's a quick guide on what's trending and why:
#Soleimani - who was he?
Qasem Soleimani was sometimes touted as a future Iranian president, but in many ways his position was even more powerful.
As the leader of an elite unit of the country's military, he was responsible for expanding Iran's influence across the entire Middle East.
He led military operations in Syria, Lebanon and Iraq. He was a hugely influential figure abroad and with almost rock-star status among many people in his home country.
But the US has called the commander and his military force "terrorists" and holds them responsible for the deaths of hundreds of US personnel.
His death has provoked huge anger in Iran and worries internationally about what might happen next.
No, this doesn't have anything to do with the Scottish rock band.
Plenty of parallels are being drawn between the death of General Soleimani and another killing 105 years ago.
In June 1914, Archduke Franz Ferdinand was shot dead - along with his wife - in Sarajevo, Bosnia.
He was the heir to the Austro-Hungarian empire.
He was assassinated by an 18 year-old Bosnian activist who was furious that the country had been taken over by the Archduke's empire.
Following the shooting, countries scrambled to take sides and it started off a chain of events which led to World War One.
It was President Trump who ordered the strike and he tweeted an image of the US flag shortly after the news broke.
It's led to a lot of chatter online about some of his past tweets.
Back in 2011, he claimed President Obama would "start a war with Iran" to get himself re-elected.
With a US presidential election coming up later this year, many commentators find the timing of this drone strike significant.
But the BBC's security correspondent Frank Gardner points out there was provocation.
"A few days ago, a huge mob in Baghdad tried to storm the US Embassy. And that was being whipped up by the militia leaders, backed by Iran.
"There was a risk if they hadn't been driven back by US Marines with tear gas that they could even have actually taken over the US Embassy."
Given the obvious parallels with Sarajevo 1914 - a single strike bringing existing tensions to boiling point - there's a lot of speculation about what might happen next.
"Iran will certainly retaliate for this. They've already vowed revenge, and they'll do it at their time of choosing," says Frank.
"It's quite a tense time now... they've declared three days of mourning, there will be huge crowds chanting 'Death to America' and probably death to us as well, Britain."
So where might that revenge come? In the West, or on Western targets in Iraq itself or other parts of the region?
Frank believes if there is retaliation, the latter option is the most likely.
"Let's hope it doesn't happen at all but if it does it's most likely to be in the region.
"They [Iran] have got very sophisticated car bomb technology. They've also got drone technology. And I think if they start to kill US servicemen in the region that will be a red line for President Trump, and he will escalate things even further."