Bono has suffered a health scare after experiencing heart palpitations while on holiday in the south of France.
The star spent a number of hours at the Princess Grace Memorial Hospital in Monaco but fans will be relieved to hear he wasn't kept in overnight.
The health scare came shortly after Bono had finished an exhausting world tour -- during which the band played to 7.1 million fans in 30 countries -- and was enjoying his summer holidays with family and friends.
"As I understand it he was seen by a doctor -- he is okay now but he got a fright," said a source.
After 48 hours of medical tests last Wednesday and Thursday, the U2 singer was spotted unwinding in Monaco's exclusive nightspot Saas Cafe last Friday night.
Renowned for his partying, Bono uncharacteristically left early in a new Audi A8 while his pals Lennon and Rocha followed in a Mercedes behind.
Bono and Ali have a villa in Eze-sur-Mer, an exclusive village of billionaires just outside the Monaco tax haven.
It is understood that the Beautiful Day singer was examined by a top heart specialist and told to get plenty of rest.
The hospital visit comes only months after a separate health scare when the rocker was forced to undergo emergency back surgery for an injury sustained during training for the band's physically demanding tours.
The star was said to have been in great form after recently attending a party in Tinakilly House in Co Wicklow before returning with Ali to the south of France.
The U2 frontman is renowned for his socialising on the French Riviera, inviting celebrities from far and wide to his luxury mansion, which he co-owns with The Edge.
The duo have been mingling with A-listers on the French playground for the rich and famous since 1993, when they splashed out a reported €3.8m on the coral-coloured seaside pad.
The rocker hit the headlines most recently when his fortune soared after one of his Facebook stake quadrupled in value to nearly $1bn (€700m).
The U2 singer's investment firm Elevation Partners paid $210m (€146m) for a stake in Mark Zuckerberg's social networking site in November 2009.
But after another investor sold his stake, pushing up the price, Elevation's stake soared to around $975m (€670m) in value, a staggering 400 per cent increase on the initial investment.