The Scots actor held hands with his Fargo co-star, Mary Elizabeth Winstead, as his brother Colin, an ex-RAF pilot, opened proceedings by reading the war poem, High Flight.
Father-of-four McGregor, 47, announced he’d split from wife Eve Mavrakis last year after photos emerged of him kissing the 33-year-old American in a London cafe, while she also divorced her husband, Riley Stearns.
The Trainspotting star cited “irreconcilable differences” when he filed for divorce to end his 22-year marriage in January.
Although the pair were barely on speaking terms, they were reunited in May for eldest daughter Clara’s graduation.
McGregor and Winstead were expected to appear together at the London premiere of his latest film, Christopher Robin, last week but he was instead joined on the red carpet by parents Carol and James.
She was absent from the event after 22-year-old Clara called her dad’s girl-friend a “piece of trash” on social media.
Following the premiere, McGregor said he’d taken nine months off filming to spend time with his children, including Jamyan 17, Esther, 16 and seven-year-old Anouk, and for “tinkering” with old cars.
Colin, 49, joined the glamorous pair in the Royal Gallery to watch this year’s spectacle, The Sky’s the Limit, following his moving tribute to the late servicemen and women of the RAF.
The McGregor brothers this year co-presented BBC One documentary RAF at 100 as part of centenary celebrations.
Colin admitted he was “excited and slightly terrified” ahead of his big gig and tweeted: “Honour to recite High Flight to open tonight’s @EdinburghTattoo for #RAF100 in memory of the veteran friends who’ve sadly departed us in the last few months. They’ve slipped the surly bonds of earth but will be never forgotten.”
The tattoo – now in its 69th year – has welcomed more than 1,200 international performers to participate and gathers an audience of around 220,000 every year.
The Sky’s the Limit honours the history of the RAF and Scotland’s Year of Young People. The sonnet recited by the elder McGregor was written by John Gillespie Magee Jr, a Royal Canadian Air Force fighter pilot. He was killed in an accidental collision over England in 1941, just months after the poem was finished.