"his realisation" is a correct and usable phrase in written English.
It can be used to refer to an individual's understanding or awareness of something. Example: After years of denial, his realisation that his actions were hurting those around him was a turning point in his journey towards self-improvement.
He talked about his realisation that mental health is often ignored in the process of rebuilding after such disasters.
It is part of his realisation of the American dream - to succeed at every level.
Nearly as spine-chilling as our (and his) realisation that genial old Todd is going to turn him into a meth-slave.
His realisation that one of his early models is inaccurate because "in real social networks, individuals possess social identities" is presented as an Archimedean eureka moment.
Brown knows this and, in a strange kind of way, his realisation is one shared with the anarchists on the streets.
His realisation that perhaps she might have returned is masterfully handled, and a much-discussed sex scene with on-screen wife Julie Christie remains grounded yet erotic.
And really that's the point: his dawning realisation that his talent lay in life writing is what led to his phenomenal success.
… and how long it actually tookWithin just nine days of setting out to write, he had his first realisation that his 500-words-a-day goal might not work out.
At first Anwar, the principal character, is only too happy to speak freely of his bloody past but his slow realisation of the trauma he inflicted is as powerful a cinematic moment as any you will come across this year".
Foster published his paper the following year which included his canonical realisation forms.
But his mood becomes more sober as he describes his growing realisation that he couldn't stay.
