Leading Light gave Irish trainer Aidan O'Brien a record sixth Ascot Gold Cup at the Royal Ascot meeting on Thursday.

The odds on favourite gave 44-year-old O'Brien his second landmark win inside a month as he also became the first trainer to welcome home three successive Epsom Derby winners when Australia prevailed at the beginning of June.

He will be thankful to his 20-year-old son Joseph who rode a brilliant race to keep last year's winner Estimate, owned by Queen Elizabeth, in check early in the straight and then when the mare edged ahead having finally got a clear run he battled back to pass her in the dying metres.

"He's as tough as nails," said an understandably out of breath Joseph.

"He's a laid back horse but once he gets going he really knows where the winning post is."

His father once again refused to accept all the praise for his most recent record.

"I am very lucky to have the horses that I have with such amazing pedigrees and the team I work with from the lad who looks after him to the owners," said O'Brien, who had opened his account for the meeting with his filly Bracelet in the Group Two Ribblesdale Stakes earlier on Thursday.

The Queen was grinning with delight from the Royal Box and her racing manager John Warren was equally delighted with the performance given it was her first race in 243 days.

"She (Estimate) is so brave. The Queen got such joy out of her run," said Warren.

Irish outsider Missunited ran a cracker to be third in what was her trainer, Michael Winters' first ever runner at the meeting.