This picture of Pope Francis apparently talking to retired Belgian cardinal Godfried Danneels at the Synod on the Family, which began this week, is circulating on Twitter and disturbing many Catholics. This is what you need to know:

1. Five years ago, Cardinal Danneels tried to cover up a revolting case of family sex abuse.

As the National Catholic Reporter revealed on August 30, 2010:

“ Audio recordings leaked to the Belgian media this weekend reveal Belgium's Cardinal Godfried Danneels urging a sex abuse victim not to make public that his abuser was his uncle Bishop Roger Vangheluwe of Bruges, Belgium. The recordings show Danneels pressuring the young man not to force Vangheluwe to resign.

The transcript quoted by the newspaper is chilling:

“ Cardinal Danneels asks if the nephew wants Vangheluwe to resign and adds: 'But that is his decision. I can mention it but that's all. You expect me to do something that I cannot do. I don't know what more to do. Or perhaps I have to find some other way to bring this to a satisfactory conclusion.'

When the nephew stresses that the cardinal must speak to pope and that Vangeluwe must be sanctioned by the church, Cardinal Danneels responds 'Yes but... You can also ask forgiveness and, well, you can also acknowledge your own guilt.'

Nephew: 'Whose forgiveness do I have to seek? I am not the one to ask for forgiveness.'

Danneels: 'He can do that. That's correct.'

Later, Cardinal Danneels asks that the conversation not be made public and suggests to the nephew: 'You can figure that he will resign next year and that he agrees to make no more appearances on television, that sort of thing, and before you know it a year has gone by.'

Nephew: 'No! I am putting this in your hands and the two of you have to make a decision.'

[Danneels replies] 'So you can grab us and try to blackmail us, huh, and say: 'you have to do something!'

Confronted by the tape-recording, Danneels – who had recently stepped down as archbishop of Mechelen-Brussels – waffled unconvincingly about wanting to resolve a dispute in the bishop's family. He had been 'improvising', he said. Vangheluwe, inevitably, had to resign immediately in disgrace. But Danneels was also disgraced by the revelations, first carried by the Belgian newspaper De Standaard. Not only did he try to arrange a temporary cover-up of the bishop's molestation of his nephew, but he also suggested that the victim should seek forgiveness – and accused the man of attempted blackmail when he demanded that Danneels should tell Pope Benedict XVI about the abuse.

2. Knowing about the sex abuse scandal, Pope Francis has given Danneels a place of honour at the Synod on the Family

The 279 'Synod Fathers' debating the most sensitive issues of family and sexuality include 45 personally chosen by Francis. They are dominated by senior clergy whose voices he wanted heard at the synod but who did not automatically qualify for membership. Here is a screenshot of the top of the list on the Vatican website:

The placing of Danneels' name second on the list suggests the strong approval of the Pope, despite the Belgian's ultra-radical views, which include support for a church-recognised 'sort of marriage' for gay couples. This dismays senior cardinals – but they are far more worried by the sex-abuse matter. Francis knew before he made the appointment that Danneels had tried to engage in a cover-up. Yet he went ahead.

3. Cardinal Danneels has been boasting that he helped elect Francis as pope

At the launch of his authorised biography in Brussels last month, Danneels claimed to have been part of a 'mafia club' of senior cardinals opposed to Benedict XVI who wanted to ensure that a liberal pope succeeded Benedict XVI. Jorge Bergoglio was their favourite candidate. Perhaps we shouldn't read too much in to this – the papacy was hardly in the club's gift. But when I asked a senior Vatican source this week why Francis had invited Danneels to the synod – on the face of it, a grotesquely inappropriate move – he replied: 'As a thank-you for the votes he helped deliver.' That is guesswork, and assumes a degree of cynical calculation that we don't associate with Francis. I mention it because this explanation is taken seriously at such a high level within conservative circles in the Vatican.

I've touched on the Danneels scandal briefly in my article on the synod for this week's magazine. Now the matter needs to be properly investigated. Pope Francis must explain why a man who tried to conceal sex abuse within a family is a leading participant in a synod discussing the pastoral care of families.

So far, the media have shown no interest in this story. That wouldn't be the case if Benedict XVI were still pope.