The Duke and Duchess of Cambridge have joined a dazzling array of stars at the Royal Variety Performance show.
Kate, who is four months pregnant with the couple's third child, looked stunning in a bespoke Jenny Packham crystal-embellished, full-length blue gown.
Tonight, the royals will watch a stellar line-up of artists including James Blunt, Louis Tomlinson, Paloma Faith and Seal at the evening gala hosted by Miranda Hart at the London Palladium.
With 89 shows spanning 105 years, the event is held in aid of the Entertainment Artistes' Benevolent Fund of which the Queen is patron.
The evening will be hosted by Miranda Hart and will also include performances from The Killers and The Script.
The couple last attended the event in 2014 when Kate, who was then pregnant with Princess Charlotte, showed off her burgeoning bump in a black lace gown from Diane von Furstenberg - a dress also owned by Prince Harry's girlfriend and rumoured fiancée, Meghan Markle.
The Duchess of Cambridge was left in fits of the giggles as her husband was forced to join in the Royal Variety Performance audience participation.
The Duke had gamely taken part in a comedy skit from host Miranda Hart, obligingly shouting her catch-phrase 'such fun' on request.
Hart, who said compelling Prince William to participate was on her to-do list for the Royal Variety duties, said she later hoped to see his galloping - another one of her trademarks - and 'knighting me with a lightsaber'.
Harry, who is tipped to announce his engagement to Miss Markle any day now, attended back in 2015 when he met stars including Elton John and Jack White.
The Royal couple were attending the London Palladium in the Royal box, accompanied by Laurie Mansfield, life president and executive producer of the Royal Variety Charity, and Giles Cooper, chairman and executive producer of the same.
The Duchess, wearing a sparkling Jenny Packham gown, and Duke, in black tie, went straight into the auditorium in time for the national anthem, and are due to meet performers on stage after the show.
Hart kicked off the show with a reference to the Royal guests, singing 'there's no Duchess like show Duchess' during her rendition of Irving Berlin's Annie Get Your Gun classic.
She later asked whether the Duke and Duchess were suffering 'throne envy' after she sat on a grand gold and red seat on stage.
Addressing them in the invented plural of 'Your Royal Highnii', she promised more Royal audience participation to come as the night went on.
The Royal Variety Performance takes place in aid of the Royal Variety Charity, of which The Queen is Patron.
It dates back to 1912 when King George V and Queen Mary - William's great-great grandparents - agreed to attend a Royal Command Performance at the Palace Theatre in London.
The first installment was in aid of the Variety Artistes' Benevolent Fund and its proposed plans to build an extension to its Brinsworth House home for elderly entertainers.
A second royal show was performed in July 1919 and billed as a celebration of post-war peace.
It became an annual event at the suggestion of George V in 1921, when the King decreed that "the monarch or a senior member of the Royal Family, would attend an annual performance, in aid of Brinsworth House and the Royal Variety Charity, once a year thereafter".
This was to demonstrate the Royal family's "love and support for the entertainment industry and its associated charity".
Today, it is watched by an estimated 152 million viewers worldwide, bringing the cream of international talent to the London stage - making it the most successful and longest-running entertainment show in the world.
The money raised from the show helps hundreds of entertainers throughout the UK, who need help and assistance as a result of old age, ill-health, or hard times.
Traditionally, the Queen has taken it in turns with the Prince of Wales to attend the show, but Harry, William and Kate's repeated attendance is a demonstration of how the younger members of the family are increasingly stepping in to help the Queen in her tenth decade.
Charles and Camilla watched the performance in 2013, while the Queen and the Duke of Edinburgh last went in the Diamond Jubilee year of 2012.
Kate, 35, returned to royal duties in October after battling a bout of hyperemesis gravidarum, an acute form of severe morning sickness, which forced the couple to announce their baby news earlier than planned.
Bedbound at Kensington Palace, she was forced to miss Prince George's first day of school at Thomas's Battersea.
A rich royal history stretching back over a century
The origins of the Royal Variety Performance date back to 1912 when King George V and Queen Mary agreed to attend a 'Royal Command Performance' at the Palace Theatre in London, in aid of the Variety Artistes' Benevolent Fund.
In July 1919, the second Royal show was performed and was the first to be billed a 'Royal Variety Performance'. Held at London's Coliseum, the show was staged as a 'celebration of peace'.
As the official announcement expressed it, "had been commanded by The King to show his appreciation of the generous manner in which artistes of the variety stage had helped the numerous funds connected with the War".
1966 saw the entire English football team take to the stage after their World Cup triumph, and in 1967 Sandie Shaw will be remembered for changing from her stage outfit to meet Her Majesty the Queen, "A mini is fine on stage, but I am told it would be more elegant to be presented to the Queen in something a little more special!".
The 2014 Royal Variety Performance returned to the London Palladium and welcomed the Duke and Duchess of Cambridge for their first time; the Duchess being 5 months pregnant with Princess Charlotte.
The show will be remembered for the hilarious anecdotes of host Michael McIntyre who got so enthused by the audience reaction that he ran over by 40 minutes.
Highlights included Ed Sheeran and Ellie Goulding appearing on the Royal Variety for their first time, the hugely successful One Direction, Britain's Got Talent winners Collabro and the amazing Dame Shirley Bassey who proved that after all these years she is still one of the greatest female singers of all time.