Yet, over those 12 years in which we exchanged hundreds of letters, I had never met him or even seen a photograph of him. It was as if there was an invisible thread between us: he was a kindred spirit, someone who needed me just as I needed him. Perhaps it was that we both felt trapped — Alex in prison, me in the celebrity world.
I explore the unlikely and extraordinary connection we made in my new book, Dear Fiona, to highlight the injustice I believe Alex has suffered.
So how did I, a successful actress, end up corresponding with a man who was apparently a violent burglar?
I had become an actress at the age of 11, and in 1975 made the leap into adult roles in a TV series about student nurses called Angels. The following year, when I was 19, we were filming the second series and, as usual, my fan mail was forwarded to me from my agent's office.
Young stars: Fiona Fullerton with her first husband Simon MacCorkindale in 1977
One letter in particular caught my eye, written on prison-issue notepaper in immaculate handwriting from Anthony Alexandrowicz (always known as Alex), who said he was a fan of Angels and asked for a picture of me.
'Your face could launch the U.S. Navy and a couple of submarines,' he wrote. 'But my pal says just the U.S. Navy.'
Anyone who pays you a massive compliment then gives it a twist is worth getting to know, I figured, so I wrote back, enclosing some photographs of myself.
Within days I received another letter, in which Alex informed me he was serving a life sentence. He'd already completed five years of it, and would go on to serve 17 more.
I was taken aback but, I have to admit, intrigued. Telling me this so early in our correspondence was such a huge risk to take. How did he know it wouldn't bother me that much? And, come to think of it, why didn't it?
I was young then, and I suppose I didn't think about the enormity of what he was saying — I was more beguiled by the content of his letters than I was about whatever offences he might or might not have committed in the past.
So I wrote back, giving Alex a short precis of my life, including my comfortable upbringing as the only child of an Army officer and his wife.
I wrote: 'I am going to be married on July 10 to a wonderful young man called Simon MacCorkindale — do think of us on that day'.
Alex wrote back: 'I hope Simon is really going to look after you. He's the luckiest guy on God's Earth.'
Alex told me more about himself. He was British, three years older than me — I'm 55 now — grew up in Lancashire, and had a difficult childhood.
It was in his third or fourth letter to me that he explained he had been taken into care at 12, and began stealing, then house-breaking, serving time in jail.
He explained that there had been an incident some years earlier in which a man armed with a knife broke into a house and one of the occupants, a woman, was stabbed in the ensuing scuffle. Alex is adamant he played no part in the burglary.
Some hours later, the police found Alex sleeping rough, questioned him, and put pressure on him to admit to the burglary, allegedly telling him that if he didn't, his Ukrainian father might be deported.
Alex was so afraid, he naively confessed to aggravated burglary and grievous bodily harm, and was sentenced to life imprisonment on each count.
It is very rare indeed for these offences to attract life terms — which brings us to the strangest part of Alex's story.
Some years earlier, he had visited the Soviet embassy in London to try to trace his father's relatives. It seems the British intelligence services, monitoring the embassy, took photographs of Alex talking to a Russian official.