Great Britain is “in mourning” for (de luto por) the “recently departed” (= recently died) Queen Elizabeth the 2nd.
To “mourn for” is similar to “grieve for” (= llorar la pérdida de alguien). So someone who is mourning is a “mourner” (doliente) and the mortal can be described as “mournful”.
Some examples for you to contemplate:
- There is a period of national mourning in Great Britain.
- The country is in mourning for its beloved (amada) Queen, and many mourners have visted Westminster Abbey (an abbey = abadía) where the Queen ́s coffin was laid.
- The period of mourning is longer for relatives. They are “mournful” (afligado) for longer.
To mourn has other uses: it refers to regret. People mourn or regret the passing (el paso) or the disappearance of family values (la desaparición de los valores…).