The chat show host, who announced her engagement earlier this month, said that she knew straight away that Rounds was the woman that she wanted to spend the rest of her life with.
'I proposed with my head down, hand out and a huge lump in my throat,' O'Donnell told Us Weekly.
'I knew about a week after we met! But I did the smart thing and didn't propose right away. You know, I'm at the age where I just knew. I knew she was exactly what I wanted.'
The couple are planning a private spring ceremony, with a bigger reception in the summer. 'I don't want anyone to feel left out!' Rosie explained.