Jax, a bronzeman who multiple times says he's not scared to drowning, and even Jade tells Ignis that the Bronzemen do not fear drowning. It's ironic that during the Battle of King's Landing when he starts to drown he subconsciously admits he was scared of drowning, 'he would never admit it but Jax was scared to drown.'
It's personally one of my favourite moments of the book especially since Jax is such a cold character, when he's picked out of the water by Lord Harlow, who refuses to set sail because of the fire, Jax tells him "I've been set on fire". It's such a great moment that is really uncharacter-like and something he'd never admit but it's ironic because that's what actually happened.
He's also predicts his own death basically as well, ' Outside in the Smith’s Lot in King’s Landing he would die.' He doesn't say Ignis's name, indirectly mentioning him, but its ironic that he said he because as we know Ignis ends up killing Jax outside Smith's Lot, so with the power of hindsight you can read me(the author) using he as a subtle way of telling you Jax Storm was going to die not Ignis. The reader can read he as Ignis(he) or Jax(he).