US chat show host David Letterman has made an on-air apology to his wife after admitting sexual relationships with female members of his staff. CBS employee Robert "Joe" Halderman has pleaded not guilty to trying to blackmail Letterman over the affairs. On his Monday night show, Letterman vowed to mend his relationship with his wife, Regina Lasko. The host admitted she had been "horribly hurt" by his behaviour but the affairs were firmly in the past. Letterman married Lasko in March but they have been together since 1986. The couple have a six year old son, Harry. He told his audience that making it up to her was not going to be easy: "Let me tell you folks, I got my work cut out for me," Monday's Late Show was the first since he shocked his audience by revealing relationships with staff members and saying he had been the victim of a blackmail threat. Letterman, who was greeted with applause from the audience, said "a guy" had threatened to expose his relationships with staff unless a payment of $2m (£1.2m) was made. The 62-year-old host addressed the issue with a mix of comedy and seriousness. He joked: "I got into the car this morning and the navigation lady wasn't speaking to me. Ouch." But he also admitted: "If you hurt a person, it's your responsibility, you try to fix it." He then joked, "this is only phase one of the scandal, phase two - next week I go on Oprah and sob." Guests joined in with actor Steve Martin telling Letterman: "It proves that you're a human being. And we weren't really that sure before." Letterman also apologised to his staff who, he said, had been hassled by journalists: "My thanks to the staff for, once again, putting up with something stupid I've gotten myself involved in." Halderman, a producer for the real-crime show 48 Hours, pleaded not guilty on Friday to extortion charges. Credit: BBC