He has since being working closely with Halls replacement Tim Davie and Corporate Affairs Director Alice Macandrew.
And perhaps most remarkably, without losing his sense of humour, even in moments of intense pressure.
Nothing has made me prouder than leading the BBCs communications and public affairs work, he added.
John ShieldBBC
Its been a pleasure to lead such a high performing team that has consistently delivered for the BBC.
She replaces Serota as a non-executive director.
Serotas four-year term has ended and Thomsons begins on April 3.
