Christina Aguilera may have revealed the secret to her buxom figure when she waved to her fans revealing what looks like a surgery scar under her arm.

Aguilera was in Japan on Tuesday to promote her new movie 'Burlesque' and she was on a red carpet podium when she was presented with a birthday cake to celebrate her upcoming birthday on the 18th of December.

She thanked her fans by waiving to them from the podium and revealed an inch long scar under her right hand.

According to the Daily Mail, the small scar could be the result of a transaxillary endoscopic breast augmentation, a breast enlargement technique where implants are placed through an armpit incision. Medical experts say the popular method usually leaves an inch-long scar and is the preferred option for patients who want to avoid scars on the breast.

While Aguilera has never revealed if she has had breast augmentation surgery, there has been speculation of plastic surgery when, in recent years, she has shown a fuller figure.