In this article, the cooperative output regulation problem of heterogeneous multiagent systems has been investigated. It is assumed that only a few agents could know the system matrix of the exosystem and no agent knows the topological information. Under these conditions, a novel distributed online algorithm is proposed to estimate the information relevant to the topology. Based on this algorithm, a distributed event-triggered adaptive observer is designed such that each agent can observe the exosystem. It is theoretically shown that the proposed distributed controller will make the multiagent system achieve cooperative output regulation asymptotically. Finally, a simulation is presented to show the effectiveness of the result.