Lucian, me, and the twilight of a master

He was distant and shy. And then one night 25 years ago, Lucian Freud bounded up to Richard Cork and began a remarkable friendship

Lucian Freud Working at Night 2005, a photograph by David Dawson (David Dawson)

The long and productive career of the painter Lucian Freud, who died last July aged 88, is about to come under its closest scrutiny yet.

A major exhibition at the National Portrait Gallery is expected to draw immense crowds when it opens next month, Freud's draughtsmanship will be celebrated in a London gallery, and in Chichester a third show sheds light on his working practices. Yet in life, Freud was an elusive figure, determined to pursue his obsessive vision in the studio and reluctant to stray far beyond it. Notorious for his shyness in public, he was devoted to hard work – rising early and painting people who were often expected to pose for months, even years.

He never attended the openings of his own shows. So I was astonished when, one evening in the late 1980s, he introduced himself to me in the street. Leaving a private view in a London gallery, I was suddenly aware of a lean, nimble figure darting towards me. Although the night was dark, I recognised the gaunt face at once. "I just wanted to say how much I enjoyed listening to your programme with Frank", he said, referring to a recent BBC interview I had done with Frank Auerbach. The two were great friends, having grown up in Germany and emigrated to England in the wake of Hitler's rise to power. As I would discover, Freud amassed an exceptional collection of Auerbach's paintings and marvelled at his ability to talk with such clarity and intelligence. I asked if he would consider doing a BBC interview with me. "Oh, no!" he exclaimed, "I would really hate to be interviewed!" and darted away into the shadows.

So I was surprised when, a couple of years later, my phone rang and the same distinctive voice said: "Hello, it's Lucian." My interview with Francis Bacon had just appeared in The Times, and I'd referred to Freud's "masterly little portrait of Bacon", painted "from the life during nocturnal sittings almost 40 years ago." Freud told me: "You've written that I paint at night. But I paint a great deal during the day as well." As we talked, a hostility towards Bacon became clear. Once close friends, the two men had not spoken for years. I enquired whether his incisive portrait of Bacon, stolen when the Tate lent it to a show in Berlin, had been recovered. "No", Freud said stoically, "and I have a strong suspicion that it's hanging on someone's wall in Berlin. Francis has lots of admirers there, and I'm certain they stole the picture for their own private pleasure."

I never knew the true purpose of that phone call. Maybe my article about Bacon had disturbed him, reminding him of a friendship that had gone so disastrously sour. The pair's hostility probably stemmed from Freud's determination to pursue a style free from Bacon's influence. Bacon once complained that "everything Lucian does is so careful"; Freud told me that Bacon "hasn't painted anything of consequence for years".

From then on, Freud took to ringing occasionally and asking me round to his London studio in a handsome old house on Kensington Church Street. Although he was shy to begin with, and preferred showing me his new work to talking about it, the paintings were often fascinating. In 1995, he led me to a room whose walls were covered with a hailstorm of brushmarks. Below them, a paint-smeared table set with artist's materials stood ready. Nearby, an immense canvas was facing the wall. Explaining that he had just finished it, he turned it round. It was Benefits Supervisor Sleeping, in which the naked Sue Tilley rested all her fleshy weight on a lumpy sofa, seemingly in the dream world of Freud's grandfather Sigmund. I was astounded when, in 2008, the picture sold for $33.6m at Christie's in New York, setting a world record for a painting by a living artist.

By 2002, when I visited him just before his major Tate retrospective, Freud was far more willing to talk. He opened the front door in paint-spattered trousers and unlaced boots. Although in his 80th year, he was defiantly energetic as he darted around rooms or leapt upstairs. He undoubtedly benefited from the presence of David Dawson, his assistant for 20 years. A talented artist himself, Dawson also took many photographs of Freud at work, and for three years sat naked, Freud's whippet Eli beside him, for a large painting which will be one of the culminating images in the National Portrait Gallery show.

Freud was fascinated by animals, and, in 2002, had the lean agility of his dog. On a table near its basket, Rodin's dramatic bronze statue of Balzac asserted his full-length virility. Freud agreed with me that Balzac had brought out the best in Rodin, pointing out that the sculptor's local butcher posed for the figure.

Most artists hang their own work in their houses, but not Freud. All the impressive paintings displayed in the large ground-floor room, which was decorated in a neutral way and led back to a small kitchen area where Freud prepared cups of dark herbal tea, were by Frank Auerbach. The two men had remained very close, and Freud told me that "I seem to go round to dinner at Frank's about once a week". Upstairs, when Freud showed me into his bedroom on a tour of the house, did I discover a large and outstandingly powerful early painting of struggling male figures by Francis Bacon. Opposite the bed, it must have been the last image that Freud saw at night, the first he scrutinised in the morning.

By now, Freud was easy to talk to – funny, thoughtful, and full of anecdotes, recalling events and conversations from any period of his life. But he gave not one interview before the Tate show, even though the gallery would have done its best to persuade him. Freud even disliked the advance publicity, berating "all this stuff about what a great artist I am! The public can make up their own minds .... The work should speak for itself."

How did he feel about the prospect of his life's work going on show? "I feel exposed", he said, "and I'm not surprised that the French call it an exposition. I'm not a very bad-tempered person, but I do feel more jumpy than usual. I'd like to think that I could rise above it, but the very fact that I'm thinking about it at all is probably significant." I asked which paintings really stood out from his long career. After a long pause, he replied: "The ones I think are the most courageous and truth-telling. They come, increasingly, from early on. You have to know what the truth is before you can tell it. I used to show off a lot, and I never believed in the idea of being a student."

At this point, the doorbell rang and Freud sprang from his seat with amazing agility. He came back with his daughter Bella, who was carrying an exquisite, large-eyed toddler. We chatted while the boy ran around, and I realised that Freud was having quite a sociable afternoon, even though he always insisted that "I never see anyone, or go anywhere". He was, nevertheless, expert at conserving his energies for art. "I know I don't have much time left," he told me at one point. "I'm full of aches and pains, and I wake up in the middle of the night when I should be sleeping. So I want to paint as much as possible. I'd like, ideally, to die in the studio, with a brush in my hand."

'Lucian Freud Portraits': National Portrait Gallery, 9 Feb to 27 May; 'Lucian Freud Drawings': Blain/Southern, London, 17 Feb to 5 Apr; 'David Dawson: Working with Lucian Freud': Pallant House Gallery, Chichester, 28 Jan to 20 May