Name and address of candidate.
Date
Dear (Mr/Ms/Mrs/Miss Surname)
Thank you for attending the interview (or group selection event) with us on (date) at (location) for the position of (position).
You presented yourself extremely well and impressed us very much, and the interview process is still ongoing. We will be in touch as soon as possible to inform you whether we can offer you the position or not (or when and if we will need to see you again).
I thank you for the interest and enthusiasm you have shown thus far. Should you have any questions meanwhile please let me know.
Best wishes, etc