National stars such as Tom Jones, Shirley Bassey, Michael Ball and Bonnie Tyler joined an audience of around 12, 000 people for a party in Cardiff Bay.
It had already been confirmed that First Minister Carwyn Jones and singer Dame Shirley Bassey will be among Welsh mourners at Wednesday's ceremony at St Paul's Cathedral in London.
Friday night's opening will include tributes to Dame Shirley Bassey, actress Sian Phillips, soprano Dame Gwyneth Jones, composer Alun Hoddinott and the late Richard Burton.