Michael Sheen has revealed he gave up his OBE so he could air his views about the monarchy without being a "hypocrite".
The actor, 51, said the decision had been prompted by researching the history of his native Wales and its relationship with the British state for his 2017 Raymond Williams lecture.
Speaking during an interview with newspaper columnist Owen Jones, Sheen said the "crash course" had made him realise he could not both deliver his lecture and hold on to the honour.
He said: "In my research to do that lecture, I learnt a lot about Welsh history. And by the time I'd finished writing that lecture on this laptop that I'm talking to you on right now, I remember sitting there going, 'Well I have a choice – I either don't give this lecture and hold on to my OBE or I give this lecture and I have to give my OBE back'."
Sheen, from Port Talbot, said Wales and England's shared history was still a point of contention for many Welsh people.
The Prince of Wales talks with actor's Michael Sheen (left), Stephen Campbell Moore and Stephen Fry (far right) at the Odeon, Leicester Square, central London, for the European Premiere of the film 'Bright Young Things', held in aid of the Prince's Trust.
Helen Mirren and Michael Sheen arrive for the 2007 Orange British Academy Film Awards (BAFTAs) at the Royal Opera House in Covent Garden, central London.
David Frost and Michael Sheen (right) at the 2009 British Academy Film Awards at the Royal Opera House in Covent Garden, central London.
Ralf Little (left), Michael Sheen (second left), Jason Isaacs (second right) and Ben Miller (right) arriving for the First Light Movie Awards 2009 at the Odeon Leicester Square, London.
Michael Sheen and Timothy Spall arriving at the World Premiere of The Damned United, Vue Cinema, Leicester Square, London.
Actor Michael Sheen receives an OBE from Queen Elizabeth II during investitures at Buckingham Palace.
The Prince of Wales meets Alesha Dixon and Michael Sheen during The Prince's Trust & RBS Celebrate Success Awards 2009 at the Odeon Leicester Square in central London.
Actor Michael Sheen and daughter Lily with the OBE he received earlier from Queen Elizabeth II during investitures at Buckingham Palace.
(L-R) Joe Calzaghe, Michael Sheen, Woody Harrelson and Patrick Kielty celebrate winning the 2010 Socceraid match at Old Trafford
Actor Martin Sheen in a procession, starring in day three of the Passion play taking place across his hometown of Port Talbot.
Rachel Mcadams and Michael Sheen arrive at the premiere of Sleeping Beauty, part of the 64TH Cannes Film Festival, Palais De Festival, Cannes.
Actors Joanna Lumley and Michael Sheen read a manifesto for freedom for Belarus's artists and actors to draw attention to the plight of imprisoned Belarusian presidential candidate Andrei Sannikov, in London today.
(left to right) Matt Lucas, Ewan McGregor, Graham Norton, Cate Blanchett and Michael Sheen during the filming for this week's edition of The Graham Norton Show,at the London Studios in London.
(L-R) Rachel McAdams, Michael Sheen, Paul Tonkinson and Michael McIntyre in the royal box during day twelve of the 2012 Wimbledon Championships at the All England Lawn Tennis Club, Wimbledon.
(Left to right) Graham Norton, Mark Ruffalo, Amanda Holden and Michael Sheen during the filming of the Graham Norton Show at the BBC Elstree Studios, London, to be aired on BBC One on Friday evening.
Rest of the World's Michael Sheen and Gordon Ramsay lift the trophy after winning the Soccer aid charity match against England, at Old Trafford, Manchester.
Michael Sheen arriving at the Unicef UK Halloween Ball at One Mayfair in London.
Sarah Silverman and Michael Sheen arriving at the 88th Academy Awards held at the Dolby Theatre in Hollywood, Los Angeles, CA, USA, February 28, 2016.
(L-R) Michael Sheen, Morten Tyldum, Jennifer Lawrence and Chris Pratt arrives at the "Passengers" Los Angeles Premiere held at the Fox Village Theatre in Westwood, CA on Wednesday, December 14, 2016. (Photo By Sthanlee B. Mirador) *** Please Use Credit from Credit Field ***
(L-R) Michael Sheen and Sarah Silverman arrives at the "Passengers" Los Angeles Premiere held at the Fox Village Theatre in Westwood, CA on Wednesday, December 14, 2016. (Photo By Sthanlee B. Mirador) *** Please Use Credit from Credit Field ***
Owen Teale (left), and Michael Sheen greet the Prince of Wales at his Welsh home near Llandovery, Wales, where he is hosting a music & drama evening also featuring performances by students of the Royal Welsh College of Music and Drama.
Michael Sheen (left) with co-star David Tennant (right) during rehearsals for Good Omens, based on the book by Terry Pratchett, in St James's Park, central London.
The Duchess of Cornwall speaks with Michael Sheen as she attends the NHS Heroes Awards at the London Hilton Hotel.
Michael Sheen (left) and David Tennant attending the premiere of Good Omens at the Odeon Luxe Leicester Square, central London.
(left to right) Host Graham Norton, Gloria Estefan, Chris Hemsworth, David Tennant and Michael Sheen, Nick Jonas, Joe Jonas, and Kevin Jonas of the Jonas Brothers during the filming for the Graham Norton Show at BBC Studioworks 6 Television Centre, Wood Lane, London, to be aired on BBC One on Friday evening.
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He pointed towards the controversy caused by the decision to rename the second Severn crossing the Prince of Wales Bridge in 2018. A petition against the move received more than 30,000 signatures.
"These things have power," Sheen said.
"The idea of the Prince of Wales and that being an Englishman and the history of that.
"Why Edward made his son the Prince of Wales (was) because it was part of keeping down the Welsh rebellion.
"These are things that happened so long ago but these things are resonant."
Charles, the current Prince of Wales, is due to forfeit the title when he ascends the throne.
Sheen suggested it would be a "really meaningful and powerful gesture for that title to no longer be held in the same way as it has before".
Sheen, who has portrayed famous faces on screen including Tony Blair and Sir David Frost, was made an OBE in the 2009 New Year Honours for his services to drama.
He told Jones he had decided not to announce his decision to hand back the honour in 2017 as he feared some people would find it insulting.
He said: "I didn't mean any disrespect but I just realised I'd be a hypocrite if I said the things I was going to say in the lecture about the nature of the relationship between Wales and the British state."