Tenant leaving - documents to sign?

I have a tenant renting my 1 bed apartment for the last 7 months. His rent is due on the 1st of each month. He phoned me two days ago to say he wants to leave immediately but he has a friend who wants to move in (his friend it turns out is actually living there now!). So all this is ok with me.
Do I need to get the previous tenant to sign anything to say that he has left, agrees to meter readings and has had his deposit returned?

argree the meter readings and get the new tenant to pay a new deposit, sign a new lease just as if your current tenant had left and you got this new tenant by re advertising the property - don't forget to register with PRTB

you can get existing tenant to sign a receipt saying he got deposit back, template below
http://www.irishlandlord.com/index.aspx?page=documents&folder=Tenants+Moving+Out

Goo luck

Thank you Gerry.