Blur's Damon Albarn and Oasis' Noel Gallagher

The outspoken Beady Eye singer has ridiculed his sibling's decision to join Damon and his Blur bandmate Graham Coxon on stage at a Teenage Cancer Trust concert on Saturday ending their near 20-year Britpop rivalry.

Liam seemingly believes Noel's rendition of 'Tender' with his former Blur foes is as bad as his acceptance of an invitation to meet former British Prime Minister Tony Blair - who was responsible for sending Britain to war with Iraq on a false premise - at Number 10 Downing Street in 1997.

Comparing Blur to boy band Blue, the former Oasis frontman wrote on Twitter: "Don't know what's worse RKID sipping champagne with a war criminal or them backing vocals you've just done for BLUE ! LG x (sic)"

Liam, 40, and Noel, 45, have barely spoken since the guitarist quit Oasis in August 2009 following a fight with his younger brother and they have continued to publicly trade insults ever since.

Noel, Damon and Graham were joined by Paul Weller for their performance at London's Royal Albert Hall and Noel's appearance on stage provoked rapturous applause from the audience.

Oasis and Blur had a famous chart battle in August 1995 when Blur released 'Country House' and Oasis brought out 'Roll With It' in the same week - with Blur ultimately claiming the UK number one spot.

The feud intensified and Noel later stated he wished Damon and bassist Alex James would "catch AIDS and die".

The two rock stars became unlikely friends over a drink after a chance meeting a couple of years ago and even shared a table at this year's BRIT Awards.