Speculation is mounting that the identity of the secret cardinal who Pope John Paul II appointed in 2003 may never be known, but that has not stopped many mulling who he might have been.
No one knows whether the Romanian prelate Juliu Hossu was ever aware he had secretly been made a cardinal when he died under house arrest in a monastery in 1970.
The Pope may take his secret with him to the grave
Pope Paul VI had named him "in pectore" - literally "in my breast" - the previous year.
The name of the cardinal appointed in this way is not revealed publicly, even to the Pope's closest circle - often as a means of protecting the appointee in a country where the Church faces oppression.
Once his name is announced, the cardinal can start to enjoy all the privileges of his rank - backdated to the time when he was secretly appointed.
On this occasion, Cardinal Hossu died before his name was made public in 1973 - indeed his very passing may have been what spurred the revelation.
On other occasions, the pope takes the name to the grave with him, as was the case when Pope John XXIII, who named three secret cardinals, died in 1963.
Without the public revelation of "in pectore" cardinals during the pontificate in which they were appointed, they may never don a scarlet biretta and take up their place in the College of Cardinals.
It is deemed increasingly unlikely that the identity of Pope John Paul II's "in pectore" appointment of 2003 will ever be known.
It is not contained in his will, which was read out on Thursday. Even if he features in other papal documents which Vatican officials are currently sifting through, the next pope is not necessarily obliged to honour the appointment, and the name may never be announced.
This is doubtless no accident, given the finely-tuned plans otherwise laid by a Pope who knew the end was approaching.
Nonetheless, the prospect that the secret cardinal may remain just that has fuelled curiosity, rather than quelled it.
Some believe the Pope's choice is a clergyman in China, where churches are state-sanctioned and must pledge allegiance to Beijing instead of the Vatican, or Russia.
The Pope appointed a Chinese bishop "in pectore" in the first group of cardinals he named in 1979. Ignatius Kung Pin-mei was serving a 30-year prison sentence at the time. His name was only revealed publicly in 1991, after he was released and allowed to leave the country.
During his pontificate, John Paul II also secretly appointed two cardinals from the former Soviet Union, which, under communism, was officially atheist. Their names were made public in 2001.
The names currently favoured by those who like to wonder are that of Moscow Archbishop Tadeusz Kondrusiewicz, of whom the Russian Orthodox Church has been critical, and that of Hong Kong Bishop Joseph Zen Ze-Kiun.
But a third name has also been suggested - that of the Pope's closest personal secretary, Polish Archbishop Stanislaw Dziwisz, who was at his bedside when he died.
If Dziwisz was the secret cardinal, the argument goes, then announcing his status as a cardinal would have forced him to step down from his role by the Pope's side.
Those who back this theory say the appointment was designed as a personal honour, which neither man ultimately wanted to see realised.