Azure App Registration and Service Principal

Question

i already know the difference between App Registration and Service Principal in Azure.There is also a good explanation in this post Difference between "enterprise application" and "app registration" in Azure.

However when an app registration is created,an application ID and a secret or certificate is created.In same time within a tenant is created also the service principal which refers to app registration.

So my question would be,do app registration and service principal have the same secret?If the secret for app registration expires and i update it,what happens with the secret of service principal,is it also updated? And vice versa, the secret for service principal expires and i update it, what happens with the secret of app registration,is it also updated?I guess no because the service principal inherits the setting from app registration.

Any explanation about the relationship between app registration's secret and service principal'secret would be helpful.

Update 31.01.2020 i have an app registration called sp-acr-mit-pull and also a corresponding service principal which refers to this app reg. and of course both have same app id and different objectid

Now if check the endDate of app registration,it is empty

If if check the endDate of SP,it shows me the expiry date

If i perform an update of service principal via command

az ad sp credential reset --name sp-acr-mit-pull --years 2

the opposite happen,i can see the new expiry date for the app registration and the old one for the serviceprincipal.