When Arthur Rubinstein died 25 years ago this week at the age of 95, a prurient world discovered that the twinkle-eyed pianist had left his wife and family for an Englishwoman young enough to be his granddaughter.

Annabelle Whitestone woke one December morning in 1982 to find the press encamped on her doorstep and lawyers converging in hope of an estate war. "There is a terrible gap in my life," she told me then. "Arthur was a unique human being. He brought out the best in everyone."

That gap has never narrowed. "I miss everything about him," she told me last week in the Chelsea Embankment flat where she lives with the publisher Lord Weidenfeld, whom she met and married 10 years after Rubinstein died.

"Imagine being as happy as I am and having a husband like George who is the best husband in the world. But one thing doesn't detract from the other. To have such a presence (as Arthur) in one's life, it's always with you, always in you. It's not even missing now, because it's there."

To mark the 25th anniversary, Lady Weidenfeld is convening some of Rubinstein's closest friends for a day of talks and concerts at the Royal Academy of Music with the aim of rekindling the reputation of a pianist who once sold as many records as rock stars and was as much at ease in the White House as he was with his chums Picasso and Charlie Chaplin.

Annabelle has never talked in public about their relationship, treasuring its intimacy, but she is anxious now to convey his art to new listeners.

Rubinstein, born in Lodz in 1887 with a technique so natural he could never explain the sound he produced, was a bon viveur with a love for pretty women which, he declared, was put on ice from 1932 when, at 45, he married Nela, daughter of the Polish composer Emil Mlynarski, herself half his age. They had four children, and had homes in Beverly Hills and Paris.

Annabelle Whitestone was the daughter of a Royal Navy commander, who lived with her parents on Wimpole Street and walked round the corner to work at a classical music agency, where she first met Rubinstein. She met him again a year later while working for a Spanish agency in Madrid.

"The moment he arrived I was smitten," she relates. "He had enormous charisma and colossal charm. He had this talent to make you feel you were the most beautiful woman on earth, the most intelligent, the most interesting, that there was no one but you."

He was 83, she 23, and it was, she says, her first love. "When we started the affair he was quite the most attractive man I had ever met. This was not some kinky geriatric thing; he was totally ageless and with more charm, vitality and magnetism than anyone. There were many girls who were after him at the time and I knew about the relationships he'd had until then."

Talking all night, "he told me how very lonely he was. There was a basic incompatibility with his wife. They managed to get on each other's nerves. They upset each other unnecessarily." Rubinstein told her they had to be discreet - "he was very much in the public eye, a good father and grandfather, the last thing he wanted was a scandal" - but he promised that they would see each other often.

"When I realised I had fallen for him," she says, "I was desperate. I could see no solution. When he left Spain, I was inconsolable. He would call me from all over the world but I could never be quite sure when I would see him again."

She would fly to Paris or Geneva if Nela was away, while he played long tours for low fees in Saragossa, San Sebastian and Pamplona, so that Annabelle could come along.

The only people who knew about their affair were her Madrid employers and her immediate family. "Where did you go to school?" Arthur was asked by her Victorian grandmother, who turned out to be younger than her lover. Commander Whitestone, Annabelle's father, "adored Arthur, accepted him completely".

Assisting with Arthur's memoirs in the capacity of his agent, Annabelle got on well at first with Nela. Once Nela's suspicions were aroused, though, Arthur decided to leave his family. "There was animosity between me and Nela but no confrontation," says Annabelle.

She set up home with Arthur in Geneva. For her birthday each year, he took her to Israel where Golda Meir, Menachem Begin and Jerusalem mayor Teddy Kollek were his friends. "When he said the prime minister was coming for tea, I rushed round the corner and bought the most delicious cheesecake. Golda came and ate it all. Then she said, 'You know Arthur, there are only two pianists in the world - you, and my grandson.'"

After his farewell concert at the Wigmore Hall in 1976, Annabelle nursed him through gathering blindness. "He was only ill the last two years and he was totally clear right up to the end, the most marvellous company. It was no burden to look after him. It was a joy and a privilege. He was the best company in the world, amusing, bright, with it and always so considerate, appreciative and loving."

She believes that Arthur's spirit led her to meet her husband. "I would never have gone to Jerusalem for Teddy Kollek's 80th birthday if he hadn't been such a close friend of Arthur's. And that's where I met George. One has the feeling Arthur is organising the rest of my life."

Loving memories apart, the former concert agent in Annabelle feels that Rubinstein - on record and through the artists he influenced - can bring a dash of sorely needed colour and daring to today's risk-proofed classical performances. Janina Fialkowska, his last protégé, will be among those playing at the Royal Academy next month, while Daniel Barenboim is sending a video message.

Those who saw Rubinstein in concert remember his jaunty joie de vivre even in sombre Brahms. There was a brightness to the sound he made that was more than clarity; it seemed to convey an optimism that was at once irrepressible and irresistible. You left a Rubinstein recital with a smile on your lips and a skip in your step.

"He lived life to the full," says Annabelle. "He read every book he could lay hands on. He ran to exhibitions. He was only really happy when he made other people happy. I think that's what it was about his playing, how he made that sound. It was this enormous generosity."

Remembering Rubinstein is at the Royal Academy of Music, NW1 (020 7873 7300) on 22 January.

• 

  The first date debate: who picks up the bill?

  We ask two young singles where they stand on divvying up for drinks and dinner this Valentine's Day

  ---

• 

  Chris Powell: racist abuse between players was accepted in my day

  Exclusive: After high-profile allegations this season, Charlton's manager is pleased the issue is now being addressed but says the authorities still have plenty of work to do

  ---