(CNN) -- A custody hearing for singer Michael Jackson's children scheduled for Monday has been pushed back for a second time.

From left: Prince Michael Jackson II, Paris-Michael Katherine Jackson and Michael Joseph Jackson Jr.

The hearing, which was originally scheduled for July 6, has been rescheduled for July 20 at the request of Jackson's mother, Katherine Jackson, and Jackson's former wife Debbie Rowe.

Rowe is the biological mother of two of Jackson's children -- 12-year-old Michael Joseph Jackson Jr., also known as Prince Michael, and 11-year-old Paris-Michael Katherine Jackson. Jackson's third child, Prince Michael "Blanket" Jackson II, was carried by a surrogate mother, whose name has not yet been released.

Katherine Jackson was given temporary guardianship of the children by a judge several days after her son's death.

According to Michael Jackson's will filed in 2002, he wanted his children to be cared for by his mother. If Katherine Jackson, 79, is not living, Jackson said in the will, "I nominate Diana Ross as guardian."

Ross, star of the Motown singing group the Supremes, met Jackson when he was a 9-year-old sensation. The two performed together over the years and Jackson told an interviewer in 1982 he considered Ross to be one of his true personal friends.

Don't Miss

Jackson specifically left Rowe out of his will.

Rowe reportedly signed away her parental rights to the children after she and Jackson divorced in 1999, but an appeals court re-established her parental status in 2006.

Rowe has not publicly indicated whether she will challenge Jackson for custody.

All About Michael Jackson • Debbie Rowe • Motown Record Co. LP • Katherine Jackson