Stephen Colbert Leans Into 'Affair' Rumor Between Prince William & Kate Middleton

The Kate Middleton saga continues — and now, Stephen Colbert is leaning into a new salacious rumor … namely, that Prince William might allegedly be having an affair.

The ‘Late Show’ host made the Royals one of his topics on Tuesday night’s opening monologue — and he completely embraced unfounded speculation and innuendo that Bill is, perhaps, cheating … a rumor that has been floating around for a while in tabloids, etc.

The alleged “other woman” in question is Lady Rose Hanbury — the Marchioness of Cholmondeley — who’s been in William and Kate’s inner orbit, as a friend, for years.

Like we said, this has never been confirmed … but it’s been gossiped about for a long time — and now, amid Kate’s mysterious absence, it’s kicked into high gear again … with some suggesting that it somehow has something to do with why KM’s been out of the spotlight.

Colbert didn’t seem all that interested in connecting the dots — but he was happy to poke fun at the headlines that have theorized this … cracking jokes at Will and Kate’s expense.

He even made fun of a report that suggested Kate had confronted her husband about this … to which the Prince allegedly “laughed it off” and said it was much ado about nothing.

As we reported … William has been keeping calm and carrying on with his Royal duties as Kate continues to recover from her abdominal surgery behind closed doors — although, slight glimpses of her have been seen here and there ever since her procedure in January.

Of course, her failed Photoshop attempt over the weekend — which she has explicitly taken the blame for — only added more fuel to the fire on what exactly is going on with her.

Fact is … hardly anybody believes the picture was taken when Kensington Palace says it was — and with this new affair rumor now making its way into the mainstream … it’s just another layer that Will and Kate have to combat as people keep digging into theory after theory.