Breton is related to Cornish and Welsh. It is part of the Brythonic Celtic language group while Irish is related to the Goidelic branch along with Scots Gaelic and Manx. There is also quite high L21 in Normandy and the L21 in Northern France is actually older and more diverse than any found in Britain and Ireland so it was there first before coming to the Isles. All the R1b like L21 originated further east.