From A Wiki of Ice and Fire
|Alias(es)||Long Tom Costayne|
|Book(s)||A Feast for Crows (mentioned)|
He may have been Tommen Costayne, a knight who participated in the Tourney at Ashford Meadow. In this case, he would have been appointed to the Kingsguard after 209 AC and died before Ser Harlan Grandison in 281 AC.