Value of the Included Column is stored in Leaf Node?

There is SQL- script, which generated the Nonclustered Index with Included Column:

CREATE TABLE users    (       id        INT,       firstname VARCHAR(50),       surname   VARCHAR(50)    );   CREATE CLUSTERED INDEX ix_users_id    ON users (id);   CREATE NONCLUSTERED INDEX ix_users_firstname    ON users (firstname)    include (surname);   SELECT firstname,         surname  FROM   users  WHERE  firstname = 'John'; 

If I correctly understood, most of the time, Engine of my SQL Server 2019 will seek Nonclustered Index for the above SELECT query, without touching the Clustered Index. Does that mean the value of surname column is stored in Leaf Node of the Nonclustered Index? Also, that means the value of surname is duplicated because it also stored in Clustered Index.

Am I right?