Three-time F1 world champion Sir Jackie Stewart has taken ill onboard a flight to the UK from the Geneva motor show.
The 71-year-old was given first aid by stewardesses after passing out and complaining of chest pains. The plane was met by paramedics upon landing at Heathrow airport at around 12.45pm local time.
The pilot asked passengers if there were any medical personnel on the plane, stating that there was a medical emergency.
Autoblog journalists were on the plane - they report that Stewart got up to go to the toilet during the flight but never returned to his seat.
He was conscious as the plane landed and was seen chatting to paramedics as they examined him, but was taken away by ambulance for further medical examination.
Stewart's son Paul has visited him in hospital and told the BBC: "I've just spoken to him. He seemed absolutely fine. He did pass out and as a precaution was taken to hospital. Obviously we need to establish what happened.
"Hopefully he'll be checked over and it will be nothing more sinister."
It is understood that Sir Jackie was taken to Hillingdon hospital north of Heathrow airport, where he is now under observation.
He was returning from the Geneva motor show with his wife Helen.
Sir Jackie was recently announced as working with the Renault F1 team via its owner Genii Capital, bringing to an end a long-term deal as an RBS ambassador.
As well as his three F1 titles, Sir Jackie remains in the top five race winners of all time with 27 victories to his name.