The Guardian has a thoughtful piece on whether London mayor Boris Johnson and former London mayor Ken Livingstone hate each other, two days after Johnson called Livingstone a “fucking liar” on a radio program.

Both candidates, however, are perhaps most well known for their tense relationships with their own party comrades.

The Tory Johnson (above, left), delightfully off-message for most of his political career, has had a bit of a rough relationship with his old classmate David Cameron.

Livingstone (above, right) was such a rebel when he was mayor of London that Tony Blair actually kicked him out of the Labour Party.

The two squared off in a television debate Tuesday in advance of the May 3 vote.

London’s mayoral election will be just its fourth ever — Livingstone won the first two in 2000 and 2004, and Boris won the 2008 election against Livingstone.