The other reason is you

Let's take a walk

A year had passed, Adrien was still saving Paris as chat noir, Nathalie and Gabriel couldn't be happier. But something was about to change.
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G - Nathalie, my love let's take a walk
N - at this hour?
G - please, it's such a beautiful night and I want to take a walk
N - okay, I'll just grab my coat
As Nathalie left his office Adrien walked in
A - So father, you're really going to ask?
— earlier that day __
G - Adrien? Can I - um ask you something?
A - sure
G - I'm going to ask Nathalie to marry me
A - father that's wonderful!
G - I'm going to take her on a walk but I need you to do something for me
_ back to the present_

G - yes, I am
Gabriel said with a beaming smile
G - now remember what you have to do
A - of course, I'll see you there

So Nathalie and Gabriel had set out on their walk. They walked hand in hand, stopping to get some of Andrè Glaciers famous match making ice cream.

The pair now arrived under the effilé tower
N - A-Adrien? What are you doing here?
Adrien was sat on a stool in front of a grand piano
G - Nathalie, sit here I have a surprise for you
Nathalie sat on a chair that was set there by Gabriel earlier on today.
Gabriel joined Adrien at the piano as they played a duet, Nathalie placed her hands under her chin as she listened, mesmerised by the music.
As the song came to end Nathalie applauded the boys, but they weren't quite finished yet.
Adrien began to play A thousand years by Christina Perry  as a girl, presumably from Adrien's class began to sing along softly with his piano.
Gabriel arose from the piano and extended his hand to Nathalie.
G - May I have this dance, Miss Sancoeur?
Nathalie giggled as she took Gabriel's hand in her own.
The two waltzed about, it felt as though they were the only two people in the world.
Gabriel then let go of Nathalie
She looked at him confused, but her confusion soon melted away as he kissed her lips
As they parted, Gabriel got down on one knee
N - Gabriel? What are you -
G - Nathalie, my dear Nathalie. I love you so much and I have so much to thank you for.
And I want to spend the rest of my life showing you just how much I love you.
He then took Nathalie's hand he opened the ring box with another.
The ring had a blue sapphire with flecks of purple, it shimmered under the stars.

G - so, Nathalie will you make me the happiest man in Paris and become Mrs Agreste?
Will you marry me?
N- oh Gabriel, YES! Of course
She replied through happy tears
Gabriel slid the ring upon her finger as he stud up he cupped her face and their lips met.
Adrien, being the big gabenath shipper he is, cheered in the background
A - congratulations guys!
As the couple parted from their kiss, they took Adrien in their arms as they melted in one big group hug.