@Peregrina
As widely discussed at the time, the Roman Catholic church does not recognise the validity of non-Catholic marriage services.
Trust Florianus to jump in. Tell that to every Catholic who was denied a Church wedding because they wanted to marry a divorcee. Do you know any such people? Because I do. And they were furious and still are about Johnson's behaviour. (Of course it was always said that the rich would get an annulment but that is a slightly different matter.)
If the divorcees you know who were denied a church wedding were previously wed in a Roman Catholic church, then they would, according to RC doctrine, be denied a church wedding. Johnson was not previously married in a Roman Catholic church. He was married in an Anglican church.
You need to understand RC doctrine: the Roman Catholic Church teaches that Anglican clergy are not valid priests and cannot therefore conduct any of the sacraments - any marriage over which they officiate is invalid.
It is for the same reason that Roman Catholics - even Bishops and Cardinals - will not take Communion in an Anglican church as they believe that an Anglican celebrant cannot validly consecrate the host and the wine.