Spain's Queen Sofia turned 75 on Saturday, a significant milestone that comes at a time when she has stepped up her public activities without neglecting her duties to the royal family.

It also comes as her husband, King Juan Carlos, also 75, is convalescing after his most recent hip operation.

No public ceremonies are planned and the monarchy has not provided precise information about how the queen will celebrate the birthday.

It is unclear whether the entire royal family - including the king and queen; Crown Prince Felipe and his wife, Princess Letizia; their two daughters, the infantas Leonor and Sofia; and the infantas Elena and Cristina and their children - will get together for the occasion.

Princess Cristina, who lives in Switzerland with her family, was subpoenaed earlier this year in an Spanish embezzlement case involving her husband, Iñaki Urdangarin, although the summons was later suspended.

Even in her 70s, the queen remains dedicated to her foundation, which, according to its Web site, promotes education and health projects and social and humanitarian assistance projects "benefiting children, the elderly, immigrants, the disabled and those affected by natural disasters."

She also continues to be a tireless promoter of culture in all its aspects.

Sofia was born in Athens on Nov. 2, 1938, the daughter of King Paul of Greece and his wife, Frederica of Hanover; she married then-Prince Juan Carlos in the Greek capital on May 14, 1962.

Thus far this year, she has participated in nearly 100 official activities and made three official trips outside Spain: to Mozambique for a cooperation visit, to Lisbon for an international conference on missing and sexually exploited children and to New York to receive the Franklin D. Roosevelt International Disability Rights Award. EFE