On the occasion of the 18th birthday of her son Aarav, author Twinkle Khanna became emotional and penned a heart-warming post for him.

"Happy 18th birthday Aarav! Here is something I had written for you once and to keep loosening the strings and finally cutting them off this year has not been easy.

"All these years you have been as much my teacher as I have been yours. I learned optimism, kindness and wonder from you as I taught you maths, a few manners and how to switch the lights off when you leave the room.

But looking at you growing up and listening to you repeatedly tell me how much you are looking forward to your independence, I have started realising that when you finally leave my home, my world and step into your own, my lights will go off automatically and my world will be filled with a bleak darkness," she wrote on Instagram.

Twinkle also said that she's proud of Aarav.

"Though whenever you return for a visit, I will light numerous diyas and pretend that this is not a permanent power failure; we are just celebrating Diwali.

"I am already missing the little boy you were but am so proud of the man you have become," she added.

For the uninitiated, Twinkle is currently in the UK along with her husband Akshay Kumar, son Aarav and daughter Nitara. The entire family has accompanied Akshay to the UK, where he is busy shooting for "Bellbottom".

In the film, Akshay will be seen sporting a moustache. Recreating his look, the other family members celebrated Aarav's birthday by pasting fake moustaches on their upper lips.

Sharing a picture from the moustache-themed birthday affair, Twinkle wrote: "#MamaBear #MoustacheMusketeers."

In the image, we can also see Akshay's sister Alka posing for the camera.