Prince Harry will launch the 2017 Invictus Games in Toronto - with royal watchers waiting in anticipation to see if girlfriend Meghan Markle makes an appearance.
Harry will kick-start his sporting tournament at a two-hour event welcoming athletes and their families from 17 nations.
But speculation is high he will be joined at some point during his nine-day visit to Canada for the Games, by his US actress partner, who lives and works in Toronto.
Suits star Markle, who has been dating the Queen's grandson for just over a year, revealed her love for the prince in an interview with Vanity Fair magazine, prompting speculation the announcement of a royal engagement was merely a formality.
The actress declared: "We're two people who are really happy and in love," adding "I hope what people will understand is that this is our time. This is for us."
The prince founded the Invictus Games, a paralympic-style competition for wounded, injured and sick former and still-serving servicemen and women, and staged the inaugural event in London in 2014.
The second tournament was held in Orlando, Florida in 2016, and the third in Toronto will see 550 competitors from 17 nations take part in 12 adaptive sports.
Before the opening ceremony, being staged in the early hours of Sunday morning, UK time, Harry will hold a bilateral meeting with US First Lady Melania Trump and separate talks with Canada's prime minister Justin Trudeau.
The prince built up a strong rapport with previous First Lady Michelle Obama, who is a staunch advocate for US military veterans and attended the opening of the 2016 Games.
Mrs Trump, a former model, is in Canada to support the large American contingent taking part in the Games, and is expected to attend the opening ceremony.
She praised the tournament earlier this week saying: "In just two short years, the Invictus Games have allowed thousands of injured and wounded servicemen and women from many different countries to participate in adaptive sports competitions - something that should be lauded and supported worldwide."
The First Lady added: "I am honoured by the opportunity to represent our country at this year's Games."
Among the performers at the opening ceremony, being staged at the Air Canada Centre, are English Soprano Laura Wright, The Tenors and Canadian singer-songwriter Alessia Cara.
During the eight-day Games, Harry will visit training sessions and watch participants competing in all 12 sports, including athletics, cycling and wheelchair basketball.
The prince will also visit a mental health and addiction teaching hospital, hand out Duke of Edinburgh International Gold Awards to young Canadians, attend a conference on military and veteran health research, and host a reception for the Invictus Games Foundation during his stay.
The high-profile closing ceremony on September 30 will feature performances by Bruce Springsteen, Bryan Adams and Kelly Clarkson.