UPDATE - 6/26@3:42PM: Here's the CBC's official press release (thanks RushFanForever).

A tribute concert celebrating the legacy of late Canadian music icon Gordon Lightfoot, who passed away last May, took place last month at Massey Hall in Toronto and Rush's Geddy Lee and Alex Lifeson made a surprise guest appearance:

... Lee and Lifeson, billed on the private performer rundown and setlist only as "L+L," were backed by Canadian Music Hall of Famers (and the evening's house band) Blue Rodeo on Lightfoot's song "The Way I Feel," complete with an acoustic guitar solo from Lifeson. ... "It was important for us to pay tribute to Gordon," Lee told Variety. "Not being folk or pop artists, Alex and I were looking for one of Gordon's songs that might better suit our style of play and we found that in 'The Way I Feel.' Its structure was loose and more open to interpretation than many of his more popular tunes." ... "After the gig, Gordon's daughter Meredith [Moon] said to us, 'Leave it to Rush to make 'The Way I Feel' sound prog,' so I think we succeeded," Lee added. Lee and Lifeson also came out for the ensemble finale, "Summerside of Life," featuring all of the evening's performers ...

The CBC announced earlier today that the concert will air on the CBC for Canada Day:

... The tribute - aptly titled Celebrating Gordon Lightfoot - brought together the forces of Allison Russell, Aysanabee, Burton Cummings, Caroline Wiles and Bob Doidge, City and Colour, Geddy Lee and Alex Lifeson, the Good Brothers and Travis Good, Julian Taylor, Kathleen Edwards, Meredith Moon, Murray McLauchlan, Serena Ryder, Sylvia Tyson, Tom Cochrane, Tom Wilson and William Prince. Blue Rodeo and the Gordon Lightfoot Band acted as the house band. ...

Celebrating Gordon Lightfoot will be available to stream as of 9AM EST on Canada Day (July 1st) on CBC Gem and CBC Music's YouTube channel, and broadcasts at 12PM on CBC Radio One and 4PM on CBC Music and CBC Listen. Geddy Lee posted some photos from the evening's festivities to his Instagram along with the following caption:

On Thursday evening at Massey Hall in Toronto, both Alex and myself had the profound pleasure of paying tribute to a true Canadian musical legend, Gordon Lightfoot. A huge thank you to the gracious members of Blue Rodeo for sharing their stage and prodigious talents with us both- a tremendous evening full of compelling performances and warm remembrances. An honour to be there. ...

You can watch some fan-shot video of the performance below or on YouTube.