The word came just a day after the family said in court documents it believed the entertainer had died without a valid will.
"My clients are now aware after filings that a will has been presented ," said L. Londell McMillan.
"His various advisers are looking for additional documents."
No further details were disclosed, and a copy of the document was not immediately available.
The existence of a will, and the likely appointment of an executor, could complicate a petition by Jackson's mother Katherine to become the administrator of his lucrative but debt-encumbered estate.
In documents filed in Superior Court, Jackson's parents say they believe their 50-year-old son died "intestate," or without a valid will.
A will almost always names an executor, and if validated, it would negate the petition of Jackson's mother to administer the estate, said John Novogrod, an estate lawyer and partner at Kramer Levin Naftalis & Frankel LLP in New York.
"If there is a will and if the will is a valid will, the whole petition to be named administrator will just fall way," Novogrod said.
He said the will could possibly be challenged on the grounds that Jackson may have been incompetent, did not understand it when it was created, or that he was unduly influenced.
Early Monday - just four days after the death of the King of Pop - lawyers for Katherine and Joe Jackson won temporary custody of Michael Jackson's three children and moved to become administrators of his estate.
Judge Mitchell Beckloff granted 79-year-old Katherine Jackson temporary guardianship of the children, who range in age from 7 to 12.
He also gave her control over some of her son's personal property that is now in the hands of an unnamed third party. But the judge did not immediately rule on her requests to take charge of the children's and Jackson's estates.
