Justin Welby, a layman who is posing as the "Archbishop of Canterbury", presided over an Anglican Eucharist at San Bartolomeo, a Catholic church in Rome, on 25 January.
He thanked Francis for allowing the simulation. Bishops and Anglican lay ministers attended the spectacle.
Later in the day, Francis received Welby in audience, accompanied by his wife Caroline.
Finally, Francis, Cardinal Koch, the Greek Orthodox Metropolitan Polykarpos of Italy and Welby, again in episcopal camouflage, and a few other prelates sang Vespers in St Paul's Basilica.
The meetings were part of the Week of Prayer for Christian Unity.
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