Wales wing Luke Morgan signs a new two-year contract that will keep him with the Ospreys until 2021.
Harlequins sign Wales hooker Scott Baldwin and Italy centre Michele Campagnaro for the 2019-20 season.
Wales Grand Slam winners are expected back when Dragons visit Ospreys in Saturday's Pro14 derby match.
Welsh Rugby Union chairman Gareth Davies says "the wheels came off" for the domestic game in Wales.
Audio & Video
Sean Holley pays tribute to Wales Grand Slam captain Alun Wyn Jones, including the suggestion the lock should become Wales' first minister.
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