A day after Britain's top Catholic official denied allegations he behaved "inappropriately" with other priests --- Cardinal Keith O'Brien is resigning his post. The 74-year-old priest cited health reasons for his decision.

Vatican watchers like Sarah De Nordwall of Catholic Voices say they're stunned by the announcement.

SOUNDBITE: Catholic Voices, Sarah De Nordwall saying:

"After all the cardinal has been such a strongly outspoken advocate for the rights of the unborn, and it's just a shame that someone with so much transparency around important issues hasn't really been very transparent about himself

Paddy Agnew of the Irish Times.

SOUNDBITE: Paddy Agnew, Vatican correspondent for The Irish Times, Paddy Agnew, Saying:

"It would be a huge surprise at any time, coming on the eve of the conclave, it's a bombshell because this is a guy who, as far as we know, until three hours ago, was going to be one of the people to elect the successor to Benedict XVI.

While O'Brien is still allowed to participate in the conclave, he says he won't be heading to Rome

Papal biographer Marco Politi says the O'Brien news points to a shift in the church.

SOUNDBITE: Papal Biographer, Marco Politi saying:

"The first one who started the domino effect was Pope Benedict with his resignation. And certainly he has began during his papacy a move towards cleanness and transparency in sex abuse scandals."

More than 100 Cardinals are due to arrive in Rome later this week when the Pope officially steps down.