'I met a little girl at the premiere after-party, we were chatting and I said: 'How are you, what are you doing here?' said Garner, 38, on US TV programme, Live With Regis and Kelly.
'She said: 'I met Russell on the street and he brought me in and told me to come see the movie.'
'He's just sweet that way,' added Garner about the ex-bad boy Brand.
Garner, who is married to Ben Affleck, admitted that she had not even seen Arthur until the premiere on Tuesday night.
'It was really good,' she said.
'You know how you are always shocked when you like something you are in. Well I loved it.'
The actress, who is due to appear in a new movie called The Odd Life of Timothy Green, said the comedy movie made her blub.
'I really cried at the end,' she said.