According to a first aspect of embodiments herein, a method in a first network node for handling device discovery of second user equipments in a second network for Device-to-Device (D2D) communication is provided. The network node is comprised in a first network. The first network node obtains information from a second network node within the second network. The information relates to resources for sending device discovery beacon signals in a second network. The first network node sends the obtained information to a first user equipment served by the first network node. The obtained information relates to said resources for sending device discovery beacon signals in the second network. The information enables the first user equipment to discover beacon signals from the second user equipments in the second network and/or to send beacon signals to be discovered by the second user equipments in the second network.