Aamir tweeted a video on Thursday that showed how he transformed from the sincere and principled Mahavir Phogat from his blockbuster film "Dangal" to the outrageous Shakti Kumaarr for his role in "Secret Superstar".
He also wrote: "One of my toughest roles!"
The video opens with singer-actress Monali Thakur, who features in the movie as herself, saying: "I am in love with his look."
Actress Zaira Wasim, who plays Insia, comments on his "weird shoes and jeans".
Her co-star Meher Vij says the beard is different.
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The beard is the result of lots of trials and tests on various male team members.
Choreographer Sanya Malhotra calls the character an ill-mannered person who does not know how to talk to people.
Hair designer Avan Contractor promises that the character will definitely "make you laugh, he will probably piss you off and maybe even make you cry. It's something he has never done before. It's a very colourful character. We had a great time designing this look for him."
Talking about the character played by Aamir, producer and his wife Kiran Rao says: "He is a music director who is having a bad time. Such characters are not written on a daily basis."
Aamir is also seen getting himself clicked with girls. He says: "He flirts with girls also. Shakti has all the bad qualities that one can think of."
The film's writer and director Advait Chandan says: "In his (Aamir) personal life, he is very simple and organic. I think for him to wear tight T-shirts... even he had a good time."
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Aamir then emphasises on the importance of understanding the nature and thinking of his characters.
The video shows how much the team was involved in creating his look.
Aamir says: "I had a lot of fun because the character is very crazy."
Check out Aamir's video in his tweet here:
"Secret Superstar" will be out on October 19.