To say the royal tour on which Prince William has embarked on is diplomatically sensitive is quite the understatement.
When the Duke of Cambridge steps off the RAF Voyager he is using for this tour of the Middle East in Israel, he will make history.
Never before, in the complex and fraught history of the state of Israel, has a member of the British Royal Family been on an official visit.
Yes, Prince Charles has been for the odd state funeral (he went to the one for the former President Shimon Peres in 2016) but because of the sensitivities in the region – and the frequently erupting violence between the two sides - the Foreign Office has always advised the royals not to go there.
So why now?
It’s Israel’s 70th anniversary this year, and Kensington Palace simply says "it’s the right time to go". But it’s been a long time coming – many prominent Israelis have been campaigning for a visit from British royalty for many years.
After all – the argument went – they go to many countries where the leaders or governments have been criticised or where the values of democracy have been questioned.
Why should Israel, a democratic state on the edge of Europe, be prevented from hosting a member of the Royal Family?
But while this might have been deemed ‘the right time’, it has made the tour no less difficult to arrange.
William will start in Jordan and then travel to Israel and the Occupied Palestinian Territories.
Jordan is a country to which the royals have travelled often and they enjoy a good relationship with the royal family there.
But the itinerary for Israel and the West Bank has been very carefully calibrated.
Almost to the minute, the Duke of the Cambridge will spend the same amount of time on either side of the border.
So he meets the Israeli Prime Minister Benjamin Netanyahu and then he will meet the Palestinian President Mahmoud Abbas.
He will go Jerusalem and later East Jerusalem.
He will spend time in the Israel coastal city of Tel Aviv and then he will spend time in Ramallah in the West Bank.
He will also go to Yad Vashem, Israel’s official memorial to the victims of the Holocaust.
Throughout he will be accompanied by his adviser Sir David Manning, a former Ambassador to Israel who was also a foreign affairs adviser to Tony Blair.
And there is a personal connection to the region too.
On Thursday, on the Mount of Olives in Jerusalem, Prince William will pay respects to his great-grandmother, Alice of Battenburg.
Alice, the Duke of Edinburgh’s mother, was reburied here in 1988 after she was honoured by the state of Israel for protecting a Jewish family from the Nazis in Greece during World War Two.
Above all, Prince William must walk on a tightrope for the next five days. If he gets to the end of the tour without offending one side or the other, it will be a major achievement.