United Kingdom, June 17 -- Avril Lavigne has praised her ex-husband Deryck Whibley as a "legend" after the pair reunited for a performance.

The 40-year-old singer and the Sum 41 frontman, 45, wed in 2006, but they split in 2009 and their divorce was confirmed in 2010.

However, the former couple are still on good terms, and Deryck joined Avril on stage at the RFK Stadium Grounds in Washington on Sunday night (15.06.25) as she headlined the Vans Warped Tour.

Avril and Deryck performed Sum 41's song In Too Deep together to "one of the best crowds" she has experienced.

The Complicated hitmaker wrote on Instagram: "Headlined @vanswarpedtour last night and it was everything I would have expected and more! It was one of the best crowds and y...