Hi Simon,

Here,you can write 'Vous êtes arrivé/arrivée' also.

This is because the pronom "Vous" is used for two cases-

1.To refer to an adult (in a singular way)

2.To refer to a group of people (in a plural way)

So depending on the context ,

You may also use 'Vous' with 'arrivé/arrivée' if the sentence talks about a singular person

Hope this helps

-Varsha 

Thanks Varsha! I should have known that!