The Duke of Cambridge's new role as a father was the inspiration for a royal portrait of the second-in-line to the throne, due to be unveiled today.

The oil-on-canvas piece, entitled Fatherhood, was painted by Welsh artist Dan Llywelyn Hall, whose portrait of the Queen last year was criticised as looking like a Spitting Image puppet.

The picture of William measures 90cm by 60cm (3ft by 2ft) and will be revealed this afternoon at the Wales Office in Whitehall to coincide with the 100th anniversary of the outbreak of the First World War.

It depicts the Duke - who became a father to Prince George on July 22 last year - wearing a dark suit and red tie with a poppy in his left lapel, looking slightly upwards against a red background.

The work is based on a meeting at the Millennium Stadium in Cardiff when William viewed Mr Hall's portrait of the Queen called Icon, commissioned by the Welsh Rugby Union.

The artist said: "Fatherhood is a portrait about a universal theme: the concerns, hopes and aspirations of a family man.

"On the centenary of the Somme where such horror consumed the lives of over a million people it seems appropriate to support two charities that uphold the memory and acknowledge the legacy of our forefathers."

The portrait will be put up for auction at the First World War centenary sale at Bonhams on October 1, with all proceeds going to The Victoria Cross Trust and War Memorials Trust.

Frances Moreton, director of the War Memorials Trust, said: "As we approach the centenary of the First World War up to 10% of war memorials may be in need of careful repair and conservation.

"Donations such as this will enable the charity to help many more local communities appropriately cherish our shared national war memorial heritage."

Cardiff-born Hall, 33, graduated from art school in 2003 before being awarded The Sunday Times Young Artist of the Year. His portraits of First World War veterans Henry Allingham and Harry Patch were displayed at Windsor Castle and The National Portrait Gallery and are now a permanent feature in the Royal Collection and the Victoria Art Gallery in Bath.

He is also the youngest person ever to paint the Queen, though his interpretation of the monarch last year prompted a mixed reaction.

Asked to respond to the criticisms made against his work, Hall replied: ''Well I'm with Oscar Wilde on this, I would say it's the role of the artist to educate the critic and the role of the critic to educate the public.

''So for me it's just a matter of rolling with the punches."