This is practically canon. After Altissia Prompto is at Ignis arm reach in every scripted animation. He stays behind watching him, comments out loud how the area look for Ignis sake. Sweet sunshine child also completly stops complainig after that point, tries to make himself usefull for the group. Obliviously lies that he's okay in chapter 13 (come on, that kid was complaing about sore legs, bugs and other details in first chapters and now he's bruised all over and says nothing).
Even after 10 years, he keeps touching Ignis arm or shoulder, like tho show Advisor, that he's still on his side.