My question involves landlord-tenant law in the State of: WA

I recently got an ESA letter to have my pet come stay with me in my strictly no-pets apartment. I am moving out within the next 30 days into one that is pet friendly (so that I won’t have to worry about this topic anymore), but will have my pet with me during that time.

Since I will have my pet with me for the last month of my lease at the no-pet apartment, am I required to give the letter to the landlord before bringing my pet home with me? Or am I allowed to simply show them this when they question why I have a pet, etc.? I know that since I have the letter I am allowed to have a pet as prescribed, since this is the law, but am not aware of what the law is regarding notifying my landlord of having a pet due to this letter when the apartment is no-pets policy.