Heath Ledger has got some explaining to do.

The young star of "The Patriot" and "A Knight's Tale" was seen at New York's Lotus, not with Heather Graham, but with a mystery woman.

Graham was busy shooting "The Guru" in New York City, but according to witnesses, Ledger "seemed not to care about whether anyone was watching" as he and the mystery woman "were all over each other."

The pair left the club together at about 5 a.m. Graham and Ledger have been hot and heavy despite a 10-year age difference.

The two met in Prague. Graham told Talk Magazine that her Australian hunk Heath is "such an amazing person."

We bet he'll have some "amazing" answers about the chick he was hanging out with, for sure.