were more men in this island slain
by the sword's edge--as books and aged sages
confirm--since Angles and Saxons sailed here
from the east, sought the Britons over the wide seas,
since those warsmiths hammered the Welsh,
and earls, eager for glory, overran the land
The Anglo-Saxon Chronicle
In 934, for reasons unknown, conflict between Æthelstan and Constantine seems to have broken out once again, with the former marching north with an English and Welsh army. It is said that the army reached as far north as present day Aberdeenshire and was accompanied by a fleet of ships that harried Caithness. No significant battle appears to have been fought and a settlement appears to have been negotiated, with a son of Constantine given as a hostage to Æthelstan and Constantine himself accompanying the English king on his return south. On September 13th 934, Constantine acknowledged Æthelstan's overlordship.
In August 937, Olaf sailed from Dublin with his army to join forces with Constantine and Owain and so it is suggested that the Battle of Brunanburh occurred in early October of that year.