Pregnant actress GILLIAN ANDERSON is expecting a baby boy.
 
The X-Files star, 39, and her longterm boyfriend Mark Griffiths announced their baby news last month (Jun08).
 
And Anderson confirmed the sex of the new arrival to U.S. talk show host David Letterman on Monday (28Jul08) night.
 
She is scheduled to give birth in October (08).
 
The pair already has a 21-month-old son, Oscar, in addition to Anderson's teenage daughter Piper, 13, from her first marriage to Clyde Klotz.