Portland’s most ex-pensive property has sold to a private buyer after being on the market for more than £4 million.

Pennsylvania Castle, which is 210 years old, was viewed by potential buyers from Russia and Australia since it was put on the market last summer.

The famous castle was once owned by John Penn – the grandson of William Penn the man who founded the state of Pennsylvania in the USA – and then by Stephen Curtis, who had extensive business dealings as a lawyer for a Russian oligarch.

It is rumoured that the castle sold for around £3.5million to an Australian couple who will move in at the beginning of February.

The castle has seven bedrooms, eight bathrooms and a swimming pool and was on the market with Hamptons International Development.

Director Giles Muddle, of Hamptons, confirmed that the castle has sold but would not disclose the sum it was purchased for.

During the sale the agents were marketing it as a ‘real one-off for somebody that can deal with relative remoteness.’ The castle was also described as ‘a sumptuously appointed castillated mansion’ which has ‘wide sweeping views over the Jurassic Coast and English Channel towards St Alban’s Head and the Isle of Wight in the distance.’ The gardens include an Italian Garden with lily ponds, roses and an ornamental fountain.

It also has a stone table and chairs overlooking the cliff edge and the World Heritage Jurassic coast.

It also has a tropical garden, a waterfall, stocked Koi Carp pool, Japanese teahouse, a tree house, an orangery and the wine cellar.

The castle was sold by Sarah Curtis, who moved to the castle with her husband Stephen.

Stephen was buried in the grounds of his beloved castle on Portland in 2004 after he died in a helicopter crash.

Mr Curtis, who had extensive business dealings with Russian oligarchs, died when the Augusta 109 helicopter he was travelling in crashed and exploded in a fireball in a field on approach to Bournemouth International Airport.

The History of the Castle

King George III gave the land to John Penn during one of his visits to the island and the architect James Wyatt then built the castle – completing it in 1800.

Mr Penn named the 'marine mansion' after his grandfather William Penn, the founder of Pennsylvania in the USA.

The £20,000 castle was officially opened by the daughter of George III and Queen Charlotte.

During its 210 year history, it has been a Napoleonic war outlook post and a place where Winston Churchill, General Eisenhower and General de Gaulle met to finalise the D-Day plans.

When Mr Penn died in 1834, the castle was purchased by John Merrick Head, a retired solicitor from Reigate.

After being turned into a hotel in 1950 the castle was made a private residence by businessman John Hanna before being purchased by Sarah and Stephen Curtis.

Mrs Curtis once said: “There is so much that we still have to find out about its colourful and eventful history.”