C.C.
At that age, he should be old enough to understand that others do need to sleep. Could you try having a small mattress or sleeping bag right next to your bed, and explain to him that if he wakes up lonely or afraid, he is welcome to come lay in his "special place" but that he is not to wake others?
Is he in his own room? Telling time is a hard thing at that age, as well. Often a small light that comes on at a designated time with a timer that says "it's ok to get up now" can help him differentiate between the middle of the night and early morning.
Having a cup of water and a small (safe) snack beside the bed can help, too, if he's waking up hungry. Books to read if he's having trouble sleeping, or a magnadoodle, or something else that is quiet can be nice to give him something quiet to do instead of waking you up. He's probably just having trouble adjusting to being by himself after having so many others always near him in the middle of the night. Hopefully he'll settle in soon.
Best wishes.
And congrats on having such wonderful, well-attached children. You're obviously a very sensitive and responsive mama. They are lucky to have you!