Calum is maintaining to Georgia that six people were out together and all went back to Donna's for a house party
Their whirlwind romance seemed doomed after Best was spotted partying with TV babe Donna Air.
Best was pictured at the north London home of blonde Donna in the early hours of Saturday morning.
Mum of one Donna recently split from billionaire US tycoon John Dorrance IV.
Reports suggested that partyboy Calum (30) flirted with the 32-year-old Geordie presenter at swanky London celeb nightspot Mahiki.
They left separately but sexy Donna picked up the notorious charmer in her car round the corner from the club.
The pair were driven to her house as they tried to dodge photographers.
On Sunday, Best told Georgia he was with a group of people who all went back to Donna's place for a party.
A source explained to The Irish Daily Star today: "Calum is maintaining to Georgia that six people were out together and all went back to Donna's for a house party. But all the pictures in the papers were just her and him."
Calum was in touch with Georgia on Sunday and today trying to put his side of the story across and sent her a series of texts.
But Georgia told a pal: "It's always something with him, some excuse.
"At this point she just thinks he's making himself look bad. It's not as if she's sitting around bawling crying."
Calum and Georgia hooked up during the filming of Celebrity Salon during the summer.
After holiday in Jamaica and Italy already this year together, their relationship has hit a rocky patch in the last week.
According to one informed source: "When Calum is with Georgia, he is the perfect gentleman and there is genuinely a lot of love between them.
"It's when Calum goes back to London and she's at home in Dublin that he can go off the rails and lives up to his party boy reputation."
Best’s PR man Erin Daniel McKee told The Star: “There was a small group of people at the house and absolutely nothing happened with Calum and Donna.”
Calum Best said recently of his relationship with Georgia: "Yes, I'm in love and it's for the first time."
Feisty Dubliner Georgia (26) was convinced he had changed his ways.
She said last week: "I was a bit wary of him when we first met because I knew about his track record with the ladies.
"But he charmed me and I think he's a really great guy.
"I keep him in line because I'm not someone who takes any crap.
"I don't think he's used to girls like that. I'm not worried about him running off with any other women."
Calum, son of football legend George, has dated a string of women including Hollywood wildchild Lindsay Lohan and Girls Aloud’s Sarah Harding.
He also claimed last week he was a changed man, saying: “In the past I have been a very bad boy but that was in the past”.