Harry is widely expected to propose to Markle after she opened up about their relationship in an interview with Vanity Fair magazine, declaring: ''We're two people who are really happy and in love."
The Prince is likely to be marking his birthday with the American who stars in the hit legal drama Suits. The pair have been dating for just over a year after meeting through friends.
They are expected to make their first public appearance together at an official event soon when Harry heads to Markle's home city of Toronto for the 2017 Invictus Games next week.
Fifth in line to the throne, Harry will give speeches at both the opening and closing ceremonies, watch a host of sports events and carry out a number of extra engagements including visiting a mental health and addiction teaching hospital.
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The Prince, who founded the Invictus Games, a paralympic-style competition for wounded, injured and sick former and still-serving servicemen and women, will be in the Canadian city carrying out public appearances from September 22 to September 30.
:: Prince Harry - the Prince and Princess of Wales's youngest son - was born Prince Henry Charles Albert David of Wales at 4.20pm, weighing 6lb 14oz, on September 15 1984.
He came into the world at the private Lindo wing of St Mary's Hospital in Paddington, central London, in the same room where older brother Prince William was born two years earlier.
Harry's nephew and niece Prince George and Princess Charlotte of Cambridge were also born in the Lindo wing.
The Prince of Wales told crowds outside that his second son had ''pale blue eyes'' and hair of ''a sort-of indeterminate colour''.
As a youngster, Harry was only called ''Henry'' when he had been ''very, very naughty'', Charles revealed.
He has produced his fair share of ''naughtiness'' over the years. He brawled with a paparazzi photographer, dabbled with cannabis, sparked worldwide outrage by dressing up as a Nazi and stripped off in Las Vegas during a racy game of billiards.
He fought for his country in the Army, undertaking two front-line tours of duty in Afghanistan.
Now a full-time royal, he is passionate about his charitable causes, from promoting the Heads Together campaign to end stigma over mental health with the Duke and Duchess of Cambridge, to supporting military veterans.
He represented his grandmother the Queen overseas for the first time in 2012 on a successful tour to Belize, the Bahamas and Jamaica to mark her Diamond Jubilee, and again in 2016 on a two-week tour to the Caribbean which saw him play cricket, release baby turtles into the sea and get tested for HIV with superstar Rihanna to raise awareness on World Aids Day.
His openness about how he battled to cope with the death of his mother Diana, Princess of Wales in a car crash when he was just 12 and how he came close to a "complete breakdown" has won plaudits from mental health charities.
Just as he seemed to have proven himself as an accomplished statesman for modern royalty, his frankness in June 2017 over his royal duties caused a stir, with the Prince admitting to a Newsweek journalist that he once "wanted out" of the Royal Family but "decided to stay in and work out a role" for himself.
He also suggested that none of the Windsors wanted to be King or Queen.
Last month, the Prince and William marked the poignant 20th anniversary of the death of their mother, viewing the floral tributes left in her memory as Harry confessed "all of us lost somebody".