Why does my 10 month old wake up between 5-6 am?

Hi all! I’m hoping you can help me out. My 10 month old has been waking around 5 to 6 am for about a month now and I’m not sure why. He takes two naps a day, one at 9 am and one at 1ish pm. We have a four hour wake window before his bedtime which usually falls between