Why did Lady Gaga do this to her hair?

Lady Gaga is paying tribute to a friend by shaving part of her head.

The Mother Monster first shared her new look with her fans, posting a photo of the back of her head to her website, LittleMonsters.com. Although the majority of her hair is stacked high in a bun, a triangle of her head leading up from the neck has been shaved clean.

"I did it for u Terry," she tweeted, linking to her blog. "I'm sorry about ure mommy. She has princess die, but were all princess high."

So the new look — which won't be as dramatic when her hair is down — isn't for a costume or a video, it's to pay her condolences to a grieving pal. The "Terry" she refers to is famous photographer Terry Richardson (pictured in inset), a close friend of  26-year-old pop star.

Richardson lost his mother yesterday, posting on his Tumblr page on Sept. 11, "R.I.P. Annie Lomax, My Mom 1938-2012."

Richardson, a controversial fashion and celeb photographer, had documented his mother's final days with poignant candids of his gravely ill mom in the hospital.

One photo of her with breathing support was captioned, "The last picture I took of my Mom," while another showed an 18-year-old Terry celebrating his birthday with his then-healthy mother in Ojai, Calif.

Lady Gaga must have felt compelled to offer her condolences to her grieving friend.