Citing a desire to return to his native USA, where he has kept a home throughout his tenure in London, the move has to be seen as a blow to a Mayor who needs steady hands to help guide and deliver the massive transport projects which will define his term in office, support the Olympics and deliver for Londoners for years to come.
Many on the right argued during the election campaign that a Johnson mayoralty would have been well served to remove much of TfL's upper management and to bring in fresh and sympathetic blood at the top. However, time has shown that the Mayor has learned to work well with figures such as Peter Hendy and Tim O'Toole.
The Mayor's comments on the type of personality and experience he would like to see in Mr O'Toole's successor will speak volumes about the approach he expects to take in the remainder of this term (and his next, should he win) with regards to transport.
We wish Mr O'Toole, described as the capital's best public servant, all the best in his future endeavors.