Prince Harry joined Kate Middleton to honour the Antipodean soldiers who gave their lives in WWI at a ceremony in Westminster Abbey.
The Duke of Sussex, whose first child is due any day now, joined sister-in-law Kate to honour the sacrifices of Australian and New Zealand forces in the bloody Gallipoli campaign of 1915.
The Duchess of Cambridge attended the service in memory of the landings on 25 April, 1915 and all Australians and New Zealanders who have given their lives for their country.
Kate wore a turquoise Catherine Walker coat and Rosie Olivia fascinator combination along with a beaming smile as she walked alongside her brother-in-law.
Harry came dressed in a dark navy suit decorated with his military honours and a red poppy.
The prince's name was not printed in the order of service in case heavily pregnant wife Meghan gave birth.
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Prince Harry and the Duchess looked happy enough keeping one another company at the memorial event while their partners were preoccupied.
They were greeted by the Dean of Westminster Dr John Hall who shook hands with them as they entered the Abbey's west door.
Harry shared a joke with members of the Chapter of Westminster, the ecclesiastical governing body of Westminster Abbey, as he was introduced to them by the Dean.
He also chatted animatedly to Australia's High Commissioner George Brandis and New Zealand's deputy High Commissioner David Evans, as did Kate as she followed him.
Members of the Australian and New Zealand Army Corps (Anzacs) launched a naval attack on the Turkish peninsula in a bid to capture Constantinople - now Istanbul.
While a defining and glorious part of Turkish history which is generally viewed as a final hurrah for the Ottoman Empire, it was a costly and humiliating defeat for the Allies.
After thousands of Anzac landed, high cliffs, steep ridges, deep gullies and thick scrub slowed their momentum, leading to confusion in the face of well-coordinated Turkish resistance.
Relentless fighting went on for days as vast numbers of Turkish troops inflicted heavy losses from higher ground.
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On 19 May 10,000 Turks died after a heavy attack was repelled by allied machine gun fire, which led to a short armistice so both sides could bury their dead.
In August renewed attempts were made to break the then months long deadlock that had soldiers confined to squalid trenches.
The troops carried on, holding the trenches and facing the prospect of a harsh winter.
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Disease and illness were rife and as the tempo of the fighting fell away, so too did the men’s spirits.
Late summer would see one of very few successful missions for the allies when the trenches at Lone Pine were held for several days by the Anzacs, at a cost of 2,000 allied lives and 7,000 Turkish casualties.
The next few months brought no significant gains for the Anzac troops who were eventually evacuated on 20 December as the winter cold began to properly settle in.
Overall more than 120,000 Anzac, Turkish, Indian, British, French and Newfoundland soldiers died during eight bloody months of fighting.
While the campaign was strategically a failure, its legacy is the celebration of the "Anzac spirit" - courage, endurance, initiative, discipline and mateship - shown by the Antipodean troops.
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Today's service also marks a national day of remembrance for Australia and New Zealand.
Harry's last-minute addition to the royal line-up indicates Meghan is showing no signs so far of giving birth soon, with the duke able to leave his wife to attend the hour-long memorial in central London.
American former actress Meghan is likely to be at home in the couple's newly renovated Frogmore Cottage in the sanctuary of the Windsor Estate.
Harry and Kate will be joined by the Queen's cousin the Duke of Gloucester.
Meanwhile the Duke of Cambridge is in New Zealand where he paid tribute to those who lost their lives in battle by attending a service in Auckland.
The traditional church service in London will incorporate an Act of Remembrance, the Last Post and the words of modern Turkey's founder Kemal Ataturk from Anzac Cove, read by the Turkish ambassador to the UK.
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Thousands of Australians and New Zealanders gathered in Gallipoli for a day of commemoration.
They ignored threats of a bombing after a suspected ISIS member was arrested by Turkish authorities.
"I feel quite safe, I feel that if there is any concerns, that it would have been called off and they wouldn't have put us at risk," Chris King, a nurse from New Zealand, said from Anzac Cove during the dawn service.
