Watch HDToday. The singer is joined by Barry Manilow, gospel singer Yolanda Adams and “Will & Grace” star Megan Mullally. Songs include “Mary, Did You Know?” and “Have Yourself a Merry Little Christmas” (Aiken); a “Happy Holidays/White Christmas” medley (Manilow); “O Holy Night” Adams); and “I'll Be Home for Christmas” (Mullally). Also: Aiken is joined by Adams and Manilow for “Santa Claus Is Coming to Town.”