Craig Ferguson will step down as host of CBS’ “ The Late Late Show” in December when his contract with the network expires after nearly a decade as David Letterman’s companion in the 12:35 a.m. slot.

Ferguson broke the news to his studio audience at the 5 p.m. PT taping of Monday’s edition of “Late Late Show.” In a statement issued by the network he quipped: “CBS and I are not getting divorced, we are ‘consciously uncoupling,’ but we will still spend holidays together and share custody of the fake horse and robot skeleton, both of whom we love very much.”

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Ferguson’s decision comes less than a month after Letterman announced his intention to retire next year, and about two weeks after CBS tapped Stephen Colbert as his successor. Ferguson’s move was not a surprise given CBS’ decision to turn elsewhere for Letterman’s replacement. Ferguson’s last contract with CBS ensured him a windfall payout of an estimated $8 million-$10 million once the Eye opted against giving him “The Late Show” slot.

Ferguson took the helm of “Late Late Show” on Jan. 3, 2005. He was an unusual choice for a network latenight show — an actor, writer and one-time rock musician with a thick Scottish brogue and genuinely zany sense of humor. But as he found his sea legs in his first year on air, Ferguson carved a niche for a show anchored by his nightly monologue — which favored observational humor and anecdotes over one-liner jokes.

Ferguson’s view of America through the wide eyes of an immigrant helped him stand out from the rest of the latenight crowd. His openness about his life and his struggles with substance abuse, his love of his adopted homeland and his extended family endeared him to a hard-core group of fans. The emotional eulogy he delivered on-air in January 2006 following the death of his father drew attention to his unique style and was a turning point for the show.

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In 2004, CBS and Letterman’s Worldwide Pants production banner, which owned “The Late Late Show,” held a bake-off among comics and actors to fill the chair left vacant by Craig Kilborn. Ferguson was championed over such candidates D.L. Hughley and Michael Ian Black as as a breath of fresh air by producer Peter Lassally, a veteran of Johnny Carson’s “Tonight Show” who remains exec producer of “Late Late Show.”

CBS came on board as a co-production partner of “Late Late Show” two years ago as relations between Ferguson and Woldwide Pants became strained. Ferguson was never known to have had a close relationship with Letterman, despite their mutual friend in Lassally. Michael Naidus has served as Ferguson’s producer for most of his run. The oddball touches to the show in recent years have included robot skeleton sidekick Geoff, who wears a name tag sticker from “The Price is Right” (which tapes near Ferguson’s show on the CBS TV City lot) and a horse dubbed Secretariat that are regulars on the program.

Ferguson earned a Peabody Award in 2010 for a 2009 interview he conducted with South African Archbishop Desmond Tutu.

In addition to the nightly program, he has continued to tour as a standup and penned books, including memoir “American On Purpose: The Improbable Adventures of an Unlikely Patriot” and the novel “Between the Bridge and the River.”

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He was nominated for an Emmy for hosting “Late Late Show” in 2006, and he earned a Grammy nom this year for his comedy album “I’m Here to Help.”

Even before the Letterman-Colbert shuffle became official, Ferguson telegraphed his restlessness by taking a gig as host of the syndicated game show “Celebrity Name Game,” which bows in the fall from distrib Debmar-Mercury. His CBS-based Green Mountain West production banner has grown busier during the past two years, developing unscripted projects for Discovery (“Naked After Dark”), Science Channel (“I F*cking Love Science”) and Comedy Central (“Porn Project”).