My only concern would be if she/he was having nightmares or stressed and waking. So if there was some underlying concern - like a problem at school.
If not (and a lot of kids wake in the night) then I'd either make a bed on the floor or decide if you're ok to have him/her in your bed for a while.
My sister's child came into their bed around that age and did so for quite a long time. They speak of that time fondly now. My sister I think always enjoyed it - my BIL, maybe not so much. He would get out and go sleep in the kid's bed. It was this midnight shuffle every night or so.
As TF said though, it was relatively short lived and it's now a fond memory. So decide what you're ok with and I'd say knowing it will be a phase, it won't last long.
Personally - I would have a comforter on the floor (as I did with mine when they did this around age 3) and I would do sleepover nights (I still do this with one of mine, slightly older than yours). My kids enjoyed sleeping with me when dad was away, or even just for fun now and then and dad would sleep on our spare bed. Kids love that extra cuddle time with us. So maybe that's another possibility. Set it up for one night on a weekend, and say weekdays are for sleeping in your own bed (get a night light or something to add to their room if that would help keep them in bed).