"If I was planning on invading earth why would I have even told you I was alien.. and if you actually used your TARDIS database you would know the Newid's are a peaceful race, and how do you know this isn't my true form, it is not uncommon for a similar evolved species to look the same, take for instance you Timelord. On the outside you look human don't you?"
Charlie stood up and her skin began to slowly change colour, her clothes disappeared as the once human girl turned into a genderless blue humanoid. 
"Why should I be the only one answering the questions here. For all I know you could have stolen this space ship and not actually be a Timelord."
Charlie began to change again, now a human male with blonde hair and a similar age to the last person. Charlies voice changed accordingly to match his new gender. Clothes had also formed and created jeans and a t-shirt.
"So happy now"