A plane carrying Prince Edward and wife Sophie has been forced to make an emergency landing.
The Earl and Countess of Wessex were heading for a trip to Gibraltar when the British Airways flight returned to London following technical issues, it is understood.
It was due to touch down later this afternoon, with the royals due to walk down Main Street from the Convent to City Hall at 4pm.
According to the airline's tracker, flight BA940 was due to be delayed until 5.20pm after it returned to the UK.
, GBC News said: "BA Press Office tells GBC pilots on flight 490 decided to return to Heathrow as a precaution due to a minor technical issue, and the aircraft landed normally.
"It's arranging for a replacement aircraft to operate the flight and thanks customers for their patience."
The Spanish Government has protested against the Wessexes' visit to Gibraltar.
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Madrid still claims the territory as part of Spain and its future border arrangements are currently the subject of talks between Britain and the European Union.
Spanish diplomatic sources said the country's Foreign Ministry had "expressed its unease" at the visit.
Spain believes "is not appropriate" against the backdrop of ongoing negotiations for Gibraltar's post-Brexit relations with the Rock.
It comes weeks after Prince Edward blended into the crowds as he caught a train on the London Underground.
The Earl of Wessex, 58, was spotted on the Jubilee Line last month after spending the day celebrating winners of the Duke of Edinburgh’s Gold award.
As other commuters concentrated on their journeys, the Queen’s third child seemed to be in conversation with another man holding a similar umbrella.
He was seen getting on at Green Park and departed at Waterloo.
Edward and Sophie were involved in the bank holiday celebrations for the Queen's Platinum Jubilee this weekend.
Referring to today's emergency landing, a British Airways spokesman said this afternoon: "Our pilots decided to return to Heathrow as a precaution due to a minor technical issue, and the aircraft landed normally.
"The issue has now been fixed and the aircraft is due to depart again shortly. We'd like to thank customers for their patience and understanding."
A statement from from the Convent in Gibraltar said: "The Earl and Countess of Wessex's arrival in Gibraltar has been delayed slightly, after their flight was diverted safely back to the UK due to a technical issue.
"Alternative arrangements are being made for The Royal Highnesses' arrival in Gibraltar later today and the programme will be adjusted accordingly.
"Further information will be provided in due course."
