Alagna has already said he is going to sue La Scala

Alagna, who walked out in the middle of Aida last week after being heckled, began singing in the Piazza della Scala ahead of Thursday's staging of Aida.

The singer, 43, took a photograph of the opera house on his mobile phone.

"I came to take a souvenir, my last happy memory of La Scala," he told Italy's Ansa news agency.

The French-born tenor added that he did not know when he would see the famous opera venue again.

High melodrama strikes La Scala

The production of Verdi's Aida won a standing ovation when it premiered on 7 December in front of a star-studded audience, including Italian Prime Minister Romano Prodi.

However, reviews of Alagna were less kind - and it was during the second night's performance that the singer was booed, prompting him to vacate the stage.

Alagna is planning to sue La Scala if it does not allow him to re-join the opera, which is directed by Franco Zeffirelli.

But La Scala's management has said he will not sing the remaining scheduled performances, arguing that he has technically broken his contract.

"I dearly loved this theatre and its audience," said Alagna, who expressed his sorrow for the way things have turned out.

"I cancelled a very important production at Covent Garden to come here, but I came with great joy."