The British actress fell in love with Mark Demsteader's art as a schoolgirl and decided to purchase one of his works as a present to herself for her 21st birthday in April (11).
But she was left stunned when the painter asked if she would pose for him instead.
Watson explains, "There is a gallery in Oxford that I used to look in after school which exhibited Mark's work. His paintings were always my favourite. For my 21st birthday I decided to contact Mark to buy some of his work. When he asked if he could paint a series of paintings of me, I was a bit nervous about the idea at first but obviously incredibly flattered - it was an opportunity I couldn't turn down. I am Mark's biggest fan and I am hugely grateful."
And Demsteader, who has agreed to give 10 per cent of his proceeds from the pieces to charity, insists it was an honour to work with the star.
He says, "The idea behind them is to make a collection to celebrate Emma's birthday. I wanted to capture a moment in time, and by making each piece a quick snapshot, I hope to capture Emma as she reaches 21. In some way I hope these works celebrate Emma in what she has achieved already, and in all the many possibilities to come."
The collection is to be exhibited at London's Panter & Hall Gallery in June (11).