Leonor, who weighed 7.8lbs (3.54kg) and was delivered by Caesarean section at a private clinic in northern Madrid, is the couple’s first child and hence second in line to the throne. Under the Spanish Constitution, however, she would be overtaken should her parents subsequently have a son.

Her birth looked certain to boost support for a constitutional amendment being pushed by the Socialist Government of José Luis Rodríquez Zapatero to eliminate that male bias. Polls suggest that most Spaniards would back the amendment, and Prince Felipe has also made clear his support for ending an archaic 13thcentury Spanish code.

Looking tired but happy, Prince Felipe, 37, told an early-morning press conference at the Ruber Clinic that “in keeping with the logic of the times” his daughter would be his successor “if deemed so by the Cortes (parliament)”.

The birth “secures the succession and is a significant event both politically and constitutionally”, he added. The right-wing newspaper El Mundo led the calls for a constitutional change yesterday. “The birth of a daughter accentuates the need to reform the Constitution,” it argued. It was illogical that “a society that is working to eliminate all elements of sexism from its laws does not do the same with its monarchy”.

But changing the Constitution is difficult. Amendments need to be approved by two thirds of the Senate and the Congress before the dissolution of parliament, a general election and then a referendum.

The Infanta Leonor, as she will be known, was born 17 months after Prince Felipe’s marriage to Princess Letizia, 33, a divorced television journalist.News of the birth was sent by text message to the assembled royal press corps at 2.30am.

“It’s the most beautiful experience that can happen to anyone in life,” Prince Felipe later told a crowd of journalists and wellwishers who had waited for hours outside the hospital despite pouring rain. “The moment you see your child born is something exceptional.”

Later in the day King Juan Carlos and Queen Sofía visited the hospital and emerged beaming. “Everything went well and she’s a picture,” the King said of his granddaughter. “We’re delighted.” She takes after both her parents,” the Queen said.

Spanish political leaders were quick to congratulate the Royal Family, though Gaspar Llamazares, the Communist leader, qualified his wishes by emphasising that he is still a Republican.

Señor Zapatero congratulated the Prince and Princess of the Asturias — their official titles — and added: “We share with them and all citizens their joy at such a happy event.”

Leonor is the seventh grandchild of King Juan Carlos and Queen Sofía, and if she does become Queen she will be Spain’s first woman head of state since Queen Isabel II, who reigned from 1833 to 1868.

She is also the first heir to the Spanish throne to be born in Spain in 37 years. Alfonso XIII, who married Queen Victoria’s grand-daughter Victoria Eugenia, was exiled from Spain in 1931, when the Second Republic was established. General Franco, who established a dictatorship after his victory in the 1936-39 Civil War, chose Alfonso XIII’s grandson, Juan Carlos, who was born in Rome, as his successor in 1954.

In three weeks’ time, King Juan Carlos will celebrate the 20th anniversary of his accession to the throne.

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