Asking for leave...for a year?

I have been approached about a position with a well known international NPO. This position is a one year term and would be an amazing learning and overall life experience. It is not a gimme I have just been asked to interview.

I have a great job right now. It is in government and the experience would likely improve my skills directly related to my job. They do allow one year internal secondements so it's not that crazy to leave your position for a year.

Would you ask for the leave? If so, at what point would you talk to your employer.

My thought is the worst they could say is no?? For reference I have been there 8 years with very good performance reviews.

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