Well, getting The Weeknd to do a duet isn't what I expected.
How much of the X Factor budget is going into The Weeknd's bank account?
Adam Lambert is an excellent singer so I can imagine a duet with Sara being fantastic. I wonder which song they will perform though as Adam has never really had a big hit in the UK. Unless they choose a Queen track?
The Weeknd could perform I Feel It Coming and 5AM could sing Daft Punk's bit. Yeah...let's go with that.

lol
Matt Terry & James Arthur singing Say You Won't Let Go is the most predictable duet. The problem is you can't deny the song has been popular and Matt may end up getting votes because of the song he sang. Just like how people voted for Ben Haenow because he sang Thinking Out Loud with Ed Sheeran.