Having told us for months he would be staying on in Hawthorn, the decision appeared to catch almost everyone off guard, including the Liberal Party's administrative arm (which must now find a suitable candidate for the plum seat) and Premier Denis Napthine's office (which cannot afford to sacrifice any more political oxygen to difficult preselection battles after the Kew debacle).

There are two possible explanations for the late announcement. First, the former premier simply changed his mind and decided to quit after 15 years in Parliament, having reached the conclusion he would not seek a position on the front bench.

If this is the case, Baillieu was giving little away. In his statement to the media, Baillieu merely says that "on reflection" now is the right time to step aside and provide an opportunity for a "fresh face". Why now represents the "right time" when he could have made the same announcement months earlier is not clear.

This brings us to a second, more intriguing, possibility. That is, the late announcement was designed to head off factional rivals from the right who might have been eyeing off his seat.

On Monday, the Liberal Party will decide  how to conduct the process to replace Baillieu. It is possible (although not guaranteed) that a rank-and-file preselection vote will by bypassed to minimise the risk of a political mess three months from an election.

The brutal preselection brawl in March for the neighbouring seat of Kew might have influenced Baillieu's thinking. The process was an embarrassing disaster for government, with Mary Wooldridge – the candidate backed by both Baillieu and Napthine – losing the battle to former Stonnington mayor Tim Smith.

There have also been dark claims from some that the party is being white-anted by forces from the hard right.

The leaking of a private conversation in which the former premier was critical of some colleagues, discovered  on a stolen dictaphone, was seen by some as a push by the right to force Baillieu from his seat.

Under these circumstances, Baillieu, enigmatic as ever, might have been protecting his factional interests by bluffing about his intentions right up to the 11th hour.