Novelist Pratchett becomes a Sir

Sir Terry has sold more than 55 million books worldwide

Author Terry Pratchett has been knighted by the Queen at Buckingham Palace for services to literature.

Sir Terry, 60, was named in the New Year Honours list.

Best known for his hugely popular Discworld series of comic fantasy novels, he has sold more than 55 million books worldwide.

In 2007 Sir Terry was diagnosed with early-onset Alzheimer's disease and has since campaigned to raise awareness of the condition.