A new portrait of the Duke of Edinburgh is going on display this week.
Philip is depicted in his role as Colonel in Chief of the Queen's Royal Hussars in the oil portrait, commissioned by the regiment.
Artist Jemma Phipps, who has previously painted portraits of the Queen and the Prince of Wales, said the Duke seemed impressed with the work.
Ms Phipps said: "He was quite nice about it. He said: 'They should be pleased with that.' It was lovely to get some kind of comment."
The Duke is wearing a military uniform in the painting, for which he posed in the Yellow Drawing Room at Buckingham Palace last October and November.
Ms Phipps said the Duke was a delight to paint, adding: "It was really fun. I hope it shows his strong sense of duty. He also has a good sense of humour and can tell a good anecdote - he kept me on my toes.
"It was a huge honour and very enjoyable."
The first of four hour-long sittings saw the Duke posing in his military uniform, but he wore more comfortable clothing for the remaining sessions.
Ms Phipps praised him for his attitude to the sittings, saying: "He was as still as anything and so professional. He didn't move at all, which is quite a feat seeing as he is 90. Most of my sitters would probably complain, but he didn't."
The portrait will be shown at the Mall Galleries in central London as part of the Royal Society of Portrait Painters Exhibition from 3 to 18 May. It will then be transported to the regiment's officers' mess in Germany.
Royal commentator Richard Fitzwilliams, press consultant for the gallery, said of the portrait: "I would say this is absolutely superb, and one of the finest portraits that has been painted of a member of the royal family."