the 'frailness' [=(more commonly) 'frailty'] of his health
In his old age his health became increasingly 'frail'.
I could barely hear her 'frail' [='weak'] voice.
(..) What could I do when the ravens brought the news from the South... the ruin of my House, the death of my family? I was helpless... blind, frail. But... when I heard they had killed my brother's son... and his poor son... and the children! (..)2011 TvShow: Game of Thrones Title: Baelor Season: 1 Episode 9