Chastity Bono, civil rights advocate, journalist, author and musician, is in the early stages of changing his gender -- transitioning from female to male, TMZ has learned.

Bono, the child of legendary entertainers Sonny and Cher, began the process earlier this year, shortly after his 40th birthday.

"Yes, it's true -- Chaz, after many years of consideration, has made the courageous decision to honor his true identity," confirmed Bono's publicist, Howard Bragman.

"He is proud of his decision and grateful for the support and respect that has already been shown by his loved ones. It is Chaz's hope that his choice to transition will open the hearts and minds of the public regarding this issue, just as his 'coming out' did nearly 20 years ago.

We ask that the media respect Chaz's privacy during this long process as he will not be doing any interviews at this time."

A lot is involved in the sex reassignment process. Here's the lowdown, according to Dr. Gary Alter from "Dr. 90210" -- he's an expert. Here's what Chastity Bono is going through right now.

-- First step ... A psychiatrist evaluates the patient. If appropriate, the doctor prescribes male hormones.

-- The hormones change the body makeup, which includes hair growth. The clitoris also grows larger.

-- Removal of breasts. Dr. Alter said most states will recognize the person as a male once this occurs. A hysterectomy can also be performed during this process.

-- Dr. Alter said the decision about changing the genitalia can take several years, while the patient is taking hormones. Dr.
Alter says most people stop at this point.

-- Dr. Alter says if the patient goes forward, the surgeon often makes a small penis out of the clitoris and a scrotum by joining both labia majors. Testicle implants can then be inserted. The most sophisticated option is microsurgery in which skin, arteries and nerves are taken from the forearm and made into a phallus.

As for cost, Dr. Alter said it's all over the place, depending on how far the person wants to go. We've spoken to people who have had it done, and they say the full deal costs more than $100,000.

TMZ just got this statement from Neil G. Giuliano, President of the Gay & Lesbian Alliance Against Defamation (GLAAD):

"Chaz Bono's decision to live his life authentically represents an important step forward, both for him personally and for all who are committed to advancing discussions about fairness and equality for transgender people ... Coming out as transgender is an extremely personal decision and one that is never made lightly. We look forward to hearing Chaz's story in his own words in the near future.

"GLAAD encourages the media to cover this story accurately, and to avoid speculation about Chaz's story before he is ready to tell it in his own words.

"The GLAAD Media Reference Guide and the Associated Press Stylebook call on media to use the name and pronoun preferred by the transgender person -- in this case, referring to him as Chaz and using male pronouns."

Sonny Bono's widow -- Congresswoman Mary Bono -- tells TMZ she's behind Chastity Bono all the way.

Mary Bono, who followed in her late husband's Republican footsteps, says she "loves and supports Chaz."