Via a notice in the births, marriages and deaths section of the Times newspaper.
The Sherlock actor's girlfriend is indeed called Sophie Hunter, a theatre actress and director, and his parents are indeed named Wanda and Timothy and hers Katharine and Charles.
How very traditional.
The last time something similar happened was when comedian David Mitchell and polymath Victoria Coren announced their engagement, again in the Times, in March 2012.
The story did find its way on to the Times news pages, albeit in brief on page 20.
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