The Home Alone actor, 29, who had a close relationship with Michael Jackson is said to have donated sperm to help conceive Blanket with an unknown surrogate mother.
One source told The Sun: 'Deep down, I think Michael always wished Mack was his son. Creating Blanket was the next best thing.'
While Macaulay Culkin has refused to comment on the rumours, another of Jacko's pals Oliver! star Mark Lester has come forward to claim paternity of the children. Lester appeared on US television saying he believes he could be father to all three children. He took his daughter on American television to show her physical likeness to Paris Jackson.
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