He had also been a wonderful godfather: writing from all over the world, never forgetting Christmas or a birthday, taking Tristan to concerts whenever he swept through Paris. For his confirmation he had even given him a Guarneri cello, valued at thousands, which Tristan had been practising for days hoping Rannaldini might ask him to play. Tristan had also painted him a watercolour — not too much like Degas — of polo players in the Bois.

There was Rannaldini’s Mercedes. Tristan hurtled downstairs, beating the housekeeper, slithering on a rose-patterned rug across the floorboards, shyly shaking his godfather by the hand, before submitting to a warm, scented embrace.

As usual, Rannaldini was in a hurry. As a tenth-birthday present, he was taking Tristan to Verdi’s greatest opera, Don Carlos. The curtain would rise in an hour so they were cutting it fine, but first he wanted to hear Tristan play and whisked him into the library.

Here Rannaldini paused only to admire himself on the cover of Paris-Match, and clock any new artists on the dark red walls. Over the centuries, the Montignys had increased their fortune buying paintings ahead of fashion. Rannaldini had considerably bolstered his coffers by using Étienne’s eye to build up his own collection.

Opening the piano score of Don Carlos, at the great cello solo at the beginning of Act IV, he placed it on Tristan’s music stand.

‘Try this.’

Even though Tristan was sight-reading, he played with total concentration and the sad sound blossomed as his long fingers vibrated on the strings.

‘Excellent,’ cried Rannaldini in delight. ‘You work very hard. And this is excellent too,’ he added, putting Tristan’s watercolour inside the piano score. ‘I will hang it in my study. We must go.’

‘I hope you will not be bored,’ said Rannaldini, manoeuvring the Mercedes through the pre-theatre and dinner traffic at a speed that astounded even the Parisians. ‘It is long opera but very interesting. I will briefly explain story.