Tiana (It's Showtime)

As the BBC was preparing for Christmas, Sarah Alexander informed Rob Brydon that the princess had arrived, but that they seemed to have mislaid the frog, causing Brydon to exclaim frantically that they "[could not] have the princess without the frog". (NOTVALID: It's Showtime)

Behind the scenes
While never identified specifically, given the full context, the princess is clearly intended to be Tiana, one of the two titular leads of Disney's The Princess and the Frog, the terrestrial UK television premiere of which was a part of BBC One's Christmas line-up for 2012. When Alexander first mentions "the princess", a dancer wearing what appeared to be Tiana's trademark green gown could briefly be seen. It is not made clear whether this was intended to be Tiana, portrayed by a live-action actress.