Gina's disappointment was immense

[Bassim]

I am wondering if my sentence is grammatically correct.

Gina's disappointment was immense when it turned out that her fiancè was married.

 

[emsr2d2]

Hmmm. Despite the fact that BrE uses the phrase "To my immense disappointment", "Gina's disappointment was immense" sounds very odd. I would probably use the phrase I mentioned at the beginning of my post at the beginning of yours!

To her great/huge/immense disappointment/shock, Gina discovered [that] her fiancé was already married.

If you want to keep your word order, I'd probably write:
Gina was immensely disappointed when it turned out [that] her fiancé was already married.

 

[Rover_KE]

Bassim, note that 'fiancé' (from the French) has not yet become completely anglicised, so the e needs an acute accent. You mistakenly gave it a grave accent (though full marks for effort).

If in doubt, leave it out.

(The female equivalent is fiancée.)