by Free Britney at . Comments

Earlier today, Jude Law announced that he's expecting his fourth child this year, and his first with an undisclosed woman who the actor is no longer seeing.

His baby mama's name was a mystery ... until now, we think!

Alex Rodriguez, Cynthia Rodriguez and Kids

The speculation is that the girl Jude Law got pregnant is Kayleen McAdams, a makeup artist and the sister of his Sherlock Holmes co-star Rachel McAdams.

Various sites have identified her as the "secret mother."

According to reports, Jude Law and Kayleen McAdams hooked up last Christmas when he was working on the film. She is reportedly seven months pregnant and has just decided to inform him of this exciting fact recently. Ouch.

Kayleen McAdams, right, with sister Rachel McAdams.

The star said to have broken the scandalous news to his former wife, Sadie Frost, and their three kids - Rafferty, 12, Iris, 8, and Rudy, 6 - earlier this week.

Rachel is said to be "pissed" about the situation.

Yesterday, a rep for actor confirmed that "following a relationship last year, he has been advised that he is to be the father of a child due in the fall."

"Mr. Law is no longer in a relationship with the individual concerned, but he intends to be a fully supportive part of the child's life."