A trailer for Adam Lambert's cameo episode of Pretty Little Liars has appeared online.

The vocal powerhouse signed up to appear in a Halloween special of the US TV series, with filming taking place in July.

He seemed to be a hit on the show's set, with co-star Lucy Hale tweeting at the time:

"@adamlambert I officially love you."

A short trailer for the episode has now emerged online, which sees Lambert performing live to an enthusiastic mass of revellers on what looks like a train.

The full episode is scheduled to air in the US on October 23.