A dilapidated mystery portrait of a royal, held in the Bowes Museum collection in Durham since 1892, had long been considered a depiction of Queen Henrietta Maria.

But a discovery during a visit by the Public Catalogue Foundation, filmed for an episode of the Culture Show on BBC2, has shown the sophisticated oil on canvas is actually a work by master 17th century court painter Anthony van Dyck, full of the intricate drapery, colouring and expressionism which characterised the Flemish Baroque artist’s works.

Portrait of Olive Boteler Porter – the Queen’s lady in waiting, and the wife of Van Dyck’s friend and patron, Endymion Porter – intrigued Dr Bendor Grosvenor during his research for an online exhibition as part of the BBC’s vault-searching Your Paintings project.

It was recorded as a piece from the School of Van Dyck, but is one of a number of portraits Van Dyck made of different members of the Villiers family, who were related to the Duke of Buckingham. A telltale red carnation in Olive’s hair is likely to be an heraldic motif of the clan.

“The painting has now been examined by a number of Van Dyck scholars who agree that a previously unknown work by this artist has been hiding in the Museum’s picture store,” said Jane Whittaker, the Principal Keeper at the museum.

“A sympathetic programme of conservation has removed the disfiguring varnish layers, revealing the tonal subtleties of the sitter’s skin and her white satin dress, together with the quality of the drawing.

“We were delighted to welcome the Culture Show to The Bowes Museum, and equally delighted with the outcome of the research.”

The Bowes has put the painting on public show, and curators are awaiting further television time later this year, when a BBC4 documentary about automata will visit the eyecatching Silver Swan musical automaton which is one of their prized possessions.