Original: According to legend, Achaius, King of Scots (possibly coming to the aid of Óengus mac Fergusa, King of the Picts), while engaged in battle at Athelstaneford with the Saxon King Aethelstan of East Anglia, saw in the heavens the cross of St Andrew.
Simplified: One story says that Achaius, King of Scots,  was fighting King Aethelstan of East Anglia and he saw cross of St Andrew in the sky.