Aleksander Alekseevich Bobrinsky (1823-1903) by Franz Krüger, 1850
Here is a photo of him, from the same year as the painting, one can see the resemblance:
His name is rather confusing. Wikipedia and other websites refer to him as Count Alexander Alexeevich Bobrinsky, while the Hermitage website names him as Alexei Bobrinsky.
His wife was the beautiful Sofia Andreevna Bobrinskaya, née Shuvalova (17 July 1829 – 9 September 1912), whom he married in 1850 when he was 27 years old. They had five sons.
And apparently this is the count as a young man in 1842, as a 19-year-old, and another photo from 1845:
He was the brother of Vladimir Bobrinsky, see my other post here.