[aabbcc]

He knew about her from the start according to the article:

She says Rod had to be dragged to the hospital to be at the birth by Susannah's friend Chrissie Shrimpton, later Mick Jagger's model girlfriend. "He sat outside the labour room with his head in his hands saying, 'What have I done?'"
Susannah, who was 17, struggled to look after her daughter on her own for seven months - before she was put in care. Rod never visited his newborn child.

I think he was a bit of a creep not to financially support her while she was growing up - that is the responsibility of all parents, famous or not.

And why wouldn't he acknowledge her? Because her mother wasn't a famous model like the mothers of his other children? Maybe that's why he continues to pop out kids with every famous woman he's with - if he's really good to them maybe it will appease his guilty conscience for ignoring a child who really needed him.