Seeing Bob Dylan in concert is, as Forrest Gump might say, like a box of chocolates — you never know if you’re going to get the Bob who seems contemptuous of his audience and tired of his own songs, or the Dylan who adds to his inestimable legacy with another night of spine-tingling performances of classic songs.

Lately, of course, Dylan’s been on a roll, delivering a series of solid albums and continuing his Never Ending Tour, which has seen the 70-year-old rock legend hitting the road for at least 100 dates every year since 1988. The tour’s most recent leg featured co-headliner and erstwhile Dire Straits frontman Mark Knopfler, who wrapped up a string of European dates with Dylan last night in London — and joined the Bard for a show-closing duet on ‘Forever Young.’

As Rolling Stone notes, Dylan doesn’t feature many guests in his shows these days, but he made an exception for Knopfler, who’d been sitting in with Dylan’s band throughout the tour. Dylan fans are no doubt aware that this musical partnership goes way back to 1979′s ‘Slow Train Coming,’ which found Knopfler sitting in with Dylan, and continued when Knopfler manned the boards for Dylan’s 1983 release ‘Infidels.’

For Knopfler, the European jaunt with Dylan was a nice a break from recording his next solo album, which he’s been working on since early this year with longtime musical foil and fellow ex-Dire Straits member Guy Fletcher.

Watch Bob Dylan and Mark Knopfler perform ‘Forever Young’