The Oscar winning actor, 71, has been dating the German artist, who is 19 years his junior, for 12 years.
And he's finally proposed.
'We are engaged and very happy with that,' the star tells German magazine Bunte.
'She is my fiancée, and that says everything, doesn't it?'
Robert divorced his first wife Lola Van Wagenen in 1985 after 27 years together.
They have son Jamie, now 46, and two daughters, Shauna, 48, and Amy, 38.