Gillian Anderson, Partner Mark Griffiths Split

Gillian Anderson and Mark Griffiths attend the UK Premiere of "Mission: Impossible Ghost Protocol" on December 13, 2011 in London. Credit: Dave Hogan/Getty

Gillian Anderson is sadly adding longtime love Mark Griffiths to her ex files.

"Gillian Anderson and her partner Mark Griffiths have amicably separated after six years together," a rep for the actress, 43, tells Us Weekly exclusively.

The duo, who never wed, share sons Oscar, 5, and Felix, 3.

The X-Files and House of Mirth actress has been married twice before. She and film art director Clyde Kotz, with whom she shares daughter Piper, 17, divorced in 1997; the star and documentarian Julian Ozanne were married for two years before parting ways in 2006.

Following her role as Miss Havisham in a 2011 PBS miniseries adaptation of Great Expectations, Anderson has a full slate of projects in 2012: the films Mr. Morgan's Last Love, I'll Follow You Down and The Curse of the Buxom Strumpet, plus BBC miniseries The Fall.