She also explains the struggles of being both a mother and an artist. She does not bother to point out the double standards when it comes to male versus female genius – nobody expected Freud to have compromised his art by being a hands-on father – but Paul’s decision to have her mother raise her and Freud’s son, Frank, so that she could dedicate herself to her art, hung on her heavily, often inducing feelings of guilt, shame and anxiety.

None of this is strictly revelatory since these are confessions Paul already made in Self-Portrait – and in many ways Letters to Gwen John is best read as an addendum to the earlier work – but in opening up her story to include John’s, the book takes on a markedly different shape to its precursor, combining this intimate, immediate form of memoir with elements of biography and art criticism. The end result is a beguiling, singular work of art – a portrait of two lives, entwined through time and space: “Time is a strange substance,” Paul recalls her mother often declaring – complemented by a glorious selection of full colour artworks, reproductions of paintings by both Paul and John.

Most interesting of all, though, is Paul’s prose, which glints and gleams on the page. Early on in the book she claims that, as a painter, “words don’t come easily to me”. But if the process of writing was an arduous one, there is no sense of that here.

Letters to Gwen John is published by Jonathan Cape at £18.99. To order your copy for £16.99 call 0844 871 1514 or visit books.telegraph.co.uk. Celia Paul’s new exhibition, Memory and Desire, is at Victoria Miro, Gallery II, London N1 from April 6 to May 7