The gap... The gap is gone...

i have a feeling that king might go back to his old form leaving his wings out

No on contrary he probably will get a gap moe because he looks older but is a child in his heart and it's called gap moe because theres a gap between looks and personality before he just acted like a child :)

I dissaggree. Previously he looked and acted like a child, but he was always very powerful mage, the most powerful in fact, only losing to Merlin. That is a true gap - a childish child is actually a most powerful mage??!
Also, I think not only his looks matured, he himself matured here. So he won't be acting as a baby as much as before.
That being said, all 7 Deadly Sins have a certain infantility to them, acting very childish most of the time. That is also a gap, take Ban for example. He looks all rough like a bad guy, but is actually a kid with a golden heart inside. Diane - looks like a matured young lady, but has very girly personality. But King was further than that. He was a smol cute crybaby (actually a powerful mage). Now he is just like other guys, he has a gap, but just a small one.