need to take a week off internship due to deferred exams

I’m an international student who will be going back home in the summer and I have an internship back home, that ends at the end of august. however, i recently had to defer some of my final exams due to health reasons, and i will have to fly back to UK for one week in the second half of august to sit for my deferred exams. how should i bring this up with my internship company? should i be honest and tell them now about my situation and risk my internship offer being revoked, or should i continue with the internship and only tell them later on that i have to fly back for a week? does anyone have any advice on what reasons I can give them to fly back (emergencies?) and if it’s possible to work extra after i’m back from uk to make up for the week i’m gone?