P.B. Shelley, John Keats, and Lord Byron are major poets of the Romantic period.
They are often counted among the second generation Romantic poets.
Alfred Tennyson, however, belongs to the Victorian Age.
He became the Poet Laureate of England and is one of the most important Victorian poets.
Therefore, among the given options, the poet who is not a Romantic poet is:
\[
\text{Alfred Tennyson}.
\]