Michael McIntyre's Unexpected Guest wowed the audience on Saturday's episode (17 January) when he broke out into song.
The segment on the comedian's Big Show sees a member of the public led into a fake room that is actually part of the theatre, before the walls fall down and they see the audience.
Sam was told he was on a historic pub tour of London. He went to the "smallest pub" in the capital, which actually turned out to be a set on stage at the Theatre Royal in the West End.
The aspiring singer returned later in the show to perform a rendition of "Easy on Me," by Adele, before he was joined on stage by his emotional family.