The godfather of Michael Jackson's three kids says he "could be" the father of Michael Jackson's daughter, Paris .. and it sounds like he may be waging a legal fight.

Mark Lester -- a longtime friend of Jackson's -- says M.J. asked him if he would donate sperm during the time the singer was married to Debbie Rowe. He says a London clinic contacted him and he obliged with the donation.

Lester claims there's an uncanny resemblance between his 15-year-old-daughter Harriet and Paris.

Lester, who spoke with News of the World, says he is willing to take a paternity test.

Lester says he has "concerns about the welfare and upbringing of the children." Lester says he does not currently have contact with Jackson's three kids and it's "heartbreaking."

Lester did not say he's gearing up for a legal fight, but the signs are there ....

Stay tuned