Beware the jealousy of a younger brother...

When Jo Johnson joined a battered Boris for a chat in Downing Street on Wednesday night, you might have thought he’d have been there to console his brother who had endured the worst couple of days for any Prime Minister in recent memory.

Instead Bro- Jo launched an exocet, a missile aimed with deadly effect. he was resigning from Government as he could no longer support the PM.

The next day, Jo followed it up by sanctimoniously tweeting that he was torn between ‘family loyalty and the national interest’ and had no option but to step down.

We’ll have to take Jo’s word that it was an act of principle. But we could be forgiven for thinking it was pure malice. The timing could not have been worse, nor the tweet more theatrical.

Why couldn’t Jo have waited to resign at a time that would not so harm his brother? he knew there would be a General election, and that he could have gone quietly after Parliament had been dissolved.

Why did the committed Remainer accept a place in Boris’s Brexit Government in the first place? To my mind, Boris should never have offered Jo the job — it was always a huge risk.

We’ve all seen the damage — both personal and political — wrought by sibling rivalry in politics. ed Miliband stabbed his older brother David in the back for the leadership of the Labour Party in 2010, only for it to end in tears

for both of them and their poor mother. The family has never fully recovered.

The Johnsons insist nothing can shake their family bond, but even the closest of blood ties can have a bloody ending. ever since Adam and eve’s son Cain became the first murderer in the Bible, killing his brother Abel, fraternal bitterness has been especially toxic.

Often it’s because the younger brother, like Jo, is resentful after years of feeling treated as second best, the kid brother walking in big bro’s footsteps.

Jo has always been in Boris’s shadow. he may be taller, cleverer and have more hair, but he does not have Boris’s magic touch. Could that have been a cause of anger when he was growing up? Did he feel jealous when Boris achieved his goal of becoming PM?

We can’t know — but whatever the case, Jo’s untimely resignation comes across as nothing less than a calculated act of brotherly sabotage. And it’s left Boris feeling even more isolated.

One can’t help wondering whether the PM’s soon-to-be ex-wife, no-nonsense Marina, would have knocked some sense into those bone-headed Johnson boys if she had moved into Downing Street with him — and been there when they met on Wednesday night.