Is it allowed to have two supervisors at the same institution?

As clarified in the EC FAQ 16399, there can be only one supervisor per host institution. As European Fellowships have only one host institution, fellows can only have one supervisor. For Global Fellowships, an additional supervisor should also be appointed for the time spent at the associated partner for the outgoing phase. Other (senior) colleagues supporting the supervision of the fellow at the same host institution can be included as ‘mentors’ in the descriptive part of the proposal.