Billionaire philanthropist and spiritual leader Aga Khan has died at the age of 88, his charity the Aga Khan Development Network has announced.

Prince Karim Aga Khan was the 49th hereditary imam of the Ismaili Muslims, who traced his lineage directly to the Prophet Muhammad.

He "passed away peacefully" in Lisbon, Portugal, surrounded by his family, his charity said in a statement on social media.

Born in Switzerland, he had British citizenship and lived in a chateau in France.

King Charles III has been made aware of the death of the philanthropist, who was a friend of both himself and his mother, the late Queen Elizabeth II.

It is understood that the King is deeply saddened at the loss of a personal friend of many years and is in touch with the family privately.

The Aga Khan's charities ran hundreds of hospitals, educational and cultural projects, largely in the developing world.

He enjoyed a lavish lifestyle, with a private island in the Bahamas, a super-yacht and a private jet.

The Aga Khan Development Network said it offered its "condolences to the family of His Highness and to the Ismaili community worldwide".

"We continue to work with our partners to improve the quality of life for individuals and communities across the world, as he wished, irrespective of their religious affiliations or origins," it added.

The Ismailis, a Muslim sect, have a worldwide population of about 15 million, including 500,000 in Pakistan. There are also large populations in India, Afghanistan and Africa.

Prince Karim Aga Khan succeeded his grandfather as imam of the Ismaili Muslims in 1957 at the age of 20.

The prince had an estimated fortune of $1bn (£801m) in 2008, according to Forbes magazine. His inherited wealth was boosted by numerous business interests, including horse breeding.

He became a leading owner and breeder of racehorses in the UK, France and Ireland, breeding Shergar, once the most famous and most valuable racehorse in the world.

Shergar won the Derby at Epsom in 1981 by 10 lengths in the Aga Khan's emerald green racing silks with red epaulettes but was kidnapped in Ireland two years later and never found.

Despite losing his beloved horse, he told the BBC in 2011 - on the 30th anniversary of Shergar's biggest triumph - that he did not contemplate deserting his Irish breeding operation.

Of Shergar's triumph, he said: "It's a memory that can never, never go away.

"I've seen that film I don't know, tens or hundreds of times. I keep trying to analyse where this remarkable performance came from. Every time I see the film, I feel that I have learned something.

"If you're in racing, the Epsom Derby is one of the greats. It always has been, so to win a race of that quality in itself is an extraordinary privilege. To win it the way he won it was more than that.

"I had watched quite enough races to be able to determine what the jockey was feeling, how the horse was going at the time and when he came around Tattenham Corner, I couldn't believe my eyes, frankly.

"His victory up to this point in time was unique. Two things I found stunning - one was the ease with which that horse moved and second was the fact that during the finishing straight he just kept going away, going away, going away. That was really remarkable."

The Aga Khan went on to win the big race another four times with Shahrastani (1986), Kahyasi (1986), Sinndar (2000) and Harzand (2016).

Other notable successes included the 2008 Prix de l'Arc de Triomphe with the brilliant unbeaten filly Zarkava.

The prince was also the founder of the Aga Khan Foundation charity prince and gave his name to bodies including a university in Karachi, and the Aga Khan Program for Islamic Architecture at Harvard University and the Massachusetts Institute of Technology.

The Aga Khan Trust for Culture was key to the restoration of the Humayun's Tomb site in Delhi. There is an annual Aga Khan Award for Architecture.

And he founded the Nation Media Group, which has become the largest independent media organisation in East and Central Africa.