Neither would comment on their plans, but sources suggest the new agency will not be a digital specialist or direct competitor to Tribal DDB, but will instead work across a wider range of media.
Mike Parsons, currently head of Tribal DDB Amsterdam, will replace Brock as managing director of Tribal DDB and starts in November. Dan Ng, currently head of integration at DDB London, has been made the agency's planning director with immediate effect.
Brock and Dyke have worked together since 2005, when Brock joined Tribal from Agency.com. Dyke, formerly the planning director of Tribal, was made planning director of DDB London when planning was integrated across the group agencies.
Stephen Woodford, the chief executive and chairman of DDB, said: "Naturally, we will be sad to see Bill and Matt leave. Both have been a great asset to us and we wish them well. Looking forward, we have found a fantastic leader within the Tribal family in Mike Parsons, and promoted a home grown DDB talent in Dan Ng."