There are the haves and the have-yachts - and then there are those who can afford £21 million yachts.

That is the sum needed to buy the superyacht Christina O, formerly owned by shipping tycoon Aristotle Onassis, which has been put up for sale.

Built in 1943, the Christina O was bought by Onassis for 34,000 US dollars in 1954 and, after extensive and expensive renovations, he hosted star-studded parties on board during the late 1950s.

Guests included John F Kennedy, Winston Churchill, Frank Sinatra, Marilyn Monroe, Elizabeth Taylor, Richard Burton and John Wayne.

In 1956 Princess Grace and Prince Rainier held their wedding reception on the yacht.

Onassis' s love affair with opera singer Maria Callas was also played out on board but in 1968 that ended abruptly when Onassis courted President Kennedy's widow, Jackie. The couple married on the Christina O near Onassis's private island of Scorpios.

In 1975, Onassis died and the yacht was gifted to his daughter, Christina, in his will. She in turn bequeathed it to the Greek government as a presidential yacht.

More than 20 years later, Christina O was substantially renovated and finally restored to its former glory in 2001.

The 325ft (99m) vessel has a 35-strong crew and can accommodate 36 guests in 18 staterooms and the Onassis Suite.

On-board facilities include a library, sports lounge, children's playroom, fitness centre, beauty salon and massage room and jacuzzi.

The yacht has been put up for sale via Edmiston, a specialist agent in the yacht sector.

Chairman Nicholas Edmiston said: "Aristotle Onassis saw Christina O as a powerful symbol of his growing business empire.

"It really was the last word in opulence and many personalities were attracted by its ability to offer them some privacy, not just by its magnificence."