If you click on the link below, you will be brought to a page about St. Declan in which some of his miracles are mentioned.

Declan Donnelly's birth name is Declan Joseph Oliver Donnelly.

Declán of Ardmore, also called Déclán or Declan, was an early Irish saint of the Déisi Muman, who was remembered for having converted the Déisi in the late 5th century and for having founded the monastery of Ardmore in what is now Co. Waterford. (Wikipedia)

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- Declan

I think Declan Blake is a good name! You may want to consider some other middle names aswell such as:

Declan Luke

Declan Louis

Declan Reece/Rhys

Declan Frazer

Declan Jack

Hope I helped!