Complex sentence: The first Act of Union in 1536 placed St Asaph/Llanelwy in Denbighshire/Sir Dinbych, however in 1542 St Asaph/Llanelwy was placed in Flintshire/Si Fflint where it reamined until April 1974 when it became part of Clwyd.
Split into simpler sentences: The first Act of Union in 1536 placed St Asaph in Denbighshire. However, in 1542, St Asaph was placed in Flintshire, where it remained until April 1974, when it became part of Clwyd.