I know it would otherwise ruin your parents trip, but they will be pissed that you didn't tell them immediately.  
I would suggest having an excuse ready. E.g. "I wanted to wait to tell you after they confirmed it and when I could tell you in person."
That said, Good luck and best wishes to you.
			
			I would suggest having an excuse ready. E.g. "I wanted to wait to tell you after they confirmed it and when I could tell you in person."
That said, Good luck and best wishes to you.
				
		
			
	