According to Pro Wrestling Sheet, there was an altercation of some sort between Brock Lesnar and Matt Riddle during last night's Royal Rumble PPV. It's said that they were passing each other backstage when words were exchanged and it sounds like The Beast was keen to find out what the deal between them is.
As you're no doubt well-aware, Riddle has spent months trash-talking Lesnar in interviews and making it clear he wants a match with the WWE Champion. None of that has been at WWE's request and Riddle has instead been going into business for himself in an effort to get fans interested in such a bout and to then potentially make it happen.
Riddle and Lesnar were both in the Royal Rumble match but didn't cross paths and there don't appear to be any plans in place for these two to actually square off (not in the near future anyway). Riddle was also called out by Goldberg backstage last year and has seemingly stopped talking about him since.
Now, it will be interesting seeing if the same thing happens with his one-sided feud with Lesnar...