Stephen Colbert shut down his late-night comedy show this week for his ailing 91-year-old mother, sources close to the show said today.

The actor caused a stir today when he said only that he was canceling the shows due to “unforeseen circumstances.”

“They are a very private family,” said a source. “It’s not surprising that he did not want anyone to know what was going on.”

Colbert, the youngest of 11 children, is very close to his mother, according to the source.

When Colbert was 10, his father and two older brothers were killed in 1974 in the crash of an airliner — a tragedy that created an especially tight relationship with his mother.

The nature of Lorna Colbert’s ailments are not known and a spokesman for Colbert gave no details.

Comedy Central, which airs “The Colbert Report,” said the show would air repeat episodes until further notice.

The show was likely return “soon,” possibly as early as next week, according to a source close to the show.

On Monday night, he told the audience that he had just returned from a week in Charleston, SC.